Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

I think we could all benefit from a little compassion and modesty.

1. In defense of our oculoplastic colleagues, we are not the only specialty referring patients to them for temporal artery biopsies. These referrals come from primary care, neurology, rheumatology for elderly patients with headache and PMR with low suspicion for GCA and low pre-test probability guided only by the theory of "stakes too high". In reality, the pre-test probability in patients without neuro-ophthalmic manifestations is very low. Just as we do not like seeing unnecessary referrals for blurred vision after cataract surgery in patients who have not refraction or haven't tried reading glasses, our oculoplastics colleagues don't like seeing low suspicion referrals for TAB. It limits access to patients who actually need to see them and may have something urgent like cancer.
2. In 2026, why would you not use evidence based medicine tools? We are neuro-ophthalmologists with big powerful brains, big powerful eyes, and big powerful tools. I think we can do better by our patients than using out dated aforisms to guide clinical care. If you truly subscribe to the "stakes too high" theory, you must recognize that TAB has less than 100% sensitivity, with estimates in the 30-70% range depending on the paper and in the seminal paper by Grant Liu and the Bascom Palmer group in 1994, 30% had vision better than 20/200 which made it look like NAION; are you getting MRIs and TAB on every presumed NAION and PET scans in cases of negative TAB just to make sure you never miss GCA? The scientific evidence and clinical practice simply does not match the logical conclusions of "stakes too high."

I find these evidence based tools invaluable on a regular basis. They are simple, easy to use, and add quantifiable value to our clinical suspicions and hunches.

Best,

Drew

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

I think we could all benefit from a little compassion and modesty.

1. In defense of our oculoplastic colleagues, we are not the only specialty referring patients to them for temporal artery biopsies. These referrals come from primary care, neurology, rheumatology for elderly patients with headache and PMR with low suspicion for GCA and low pre-test probability guided only by the theory of "stakes too high". In reality, the pre-test probability in patients without neuro-ophthalmic manifestations is very low. Just as we do not like seeing unnecessary referrals for blurred vision after cataract surgery in patients who have not refraction or haven't tried reading glasses, our oculoplastics colleagues don't like seeing low suspicion referrals for TAB. It limits access to patients who actually need to see them and may have something urgent like cancer.
2. In 2026, why would you not use evidence based medicine tools? We are neuro-ophthalmologists with big powerful brains, big powerful eyes, and big powerful tools. I think we can do better by our patients than using out dated aforisms to guide clinical care. If you truly subscribe to the "stakes too high" theory, you must recognize that TAB has less than 100% sensitivity, with estimates in the 30-70% range depending on the paper and in the seminal paper by Grant Liu and the Bascom Palmer group in 1994, 30% had vision better than 20/200 which made it look like NAION; are you getting MRIs and TAB on every presumed NAION and PET scans in cases of negative TAB just to make sure you never miss GCA? The scientific evidence and clinical practice simply does not match the logical conclusions of "stakes too high."

I find these evidence based tools invaluable on a regular basis. They are simple, easy to use, and add quantifiable value to our clinical suspicions and hunches.

Best,

Drew

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

For those of us in the real world the thought of missing Ta is catastrophic.  If we even suspect Ta as a possible diagnosis I get a biopsy. Period. If it's negative and I still have concerns clinically I treat as Ta and get a rheumatologist consult. Maybe all neuroophthalmologists should learn to do the biopsy. It's not difficult and it doesn't take much time.  Yes it pays nothing but it's a small price to pay for the privilege of practicing an amazing specialty and sub specialty. 

I think we could all benefit from a little compassion and modesty.

1. In defense of our oculoplastic colleagues, we are not the only specialty referring patients to them for temporal artery biopsies. These referrals come from primary care, neurology, rheumatology for elderly patients with headache and PMR with low suspicion for GCA and low pre-test probability guided only by the theory of "stakes too high". In reality, the pre-test probability in patients without neuro-ophthalmic manifestations is very low. Just as we do not like seeing unnecessary referrals for blurred vision after cataract surgery in patients who have not refraction or haven't tried reading glasses, our oculoplastics colleagues don't like seeing low suspicion referrals for TAB. It limits access to patients who actually need to see them and may have something urgent like cancer.
2. In 2026, why would you not use evidence based medicine tools? We are neuro-ophthalmologists with big powerful brains, big powerful eyes, and big powerful tools. I think we can do better by our patients than using out dated aforisms to guide clinical care. If you truly subscribe to the "stakes too high" theory, you must recognize that TAB has less than 100% sensitivity, with estimates in the 30-70% range depending on the paper and in the seminal paper by Grant Liu and the Bascom Palmer group in 1994, 30% had vision better than 20/200 which made it look like NAION; are you getting MRIs and TAB on every presumed NAION and PET scans in cases of negative TAB just to make sure you never miss GCA? The scientific evidence and clinical practice simply does not match the logical conclusions of "stakes too high."

I find these evidence based tools invaluable on a regular basis. They are simple, easy to use, and add quantifiable value to our clinical suspicions and hunches.

Best,

Drew

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

For those of us in the real world the thought of missing Ta is catastrophic.  If we even suspect Ta as a possible diagnosis I get a biopsy. Period. If it's negative and I still have concerns clinically I treat as Ta and get a rheumatologist consult. Maybe all neuroophthalmologists should learn to do the biopsy. It's not difficult and it doesn't take much time.  Yes it pays nothing but it's a small price to pay for the privilege of practicing an amazing specialty and sub specialty. 

I think we could all benefit from a little compassion and modesty.

1. In defense of our oculoplastic colleagues, we are not the only specialty referring patients to them for temporal artery biopsies. These referrals come from primary care, neurology, rheumatology for elderly patients with headache and PMR with low suspicion for GCA and low pre-test probability guided only by the theory of "stakes too high". In reality, the pre-test probability in patients without neuro-ophthalmic manifestations is very low. Just as we do not like seeing unnecessary referrals for blurred vision after cataract surgery in patients who have not refraction or haven't tried reading glasses, our oculoplastics colleagues don't like seeing low suspicion referrals for TAB. It limits access to patients who actually need to see them and may have something urgent like cancer.
2. In 2026, why would you not use evidence based medicine tools? We are neuro-ophthalmologists with big powerful brains, big powerful eyes, and big powerful tools. I think we can do better by our patients than using out dated aforisms to guide clinical care. If you truly subscribe to the "stakes too high" theory, you must recognize that TAB has less than 100% sensitivity, with estimates in the 30-70% range depending on the paper and in the seminal paper by Grant Liu and the Bascom Palmer group in 1994, 30% had vision better than 20/200 which made it look like NAION; are you getting MRIs and TAB on every presumed NAION and PET scans in cases of negative TAB just to make sure you never miss GCA? The scientific evidence and clinical practice simply does not match the logical conclusions of "stakes too high."

I find these evidence based tools invaluable on a regular basis. They are simple, easy to use, and add quantifiable value to our clinical suspicions and hunches.

Best,

Drew

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

For those of us in the real world the thought of missing Ta is catastrophic.  If we even suspect Ta as a possible diagnosis I get a biopsy. Period. If it's negative and I still have concerns clinically I treat as Ta and get a rheumatologist consult. Maybe all neuroophthalmologists should learn to do the biopsy. It's not difficult and it doesn't take much time.  Yes it pays nothing but it's a small price to pay for the privilege of practicing an amazing specialty and sub specialty. 

I think we could all benefit from a little compassion and modesty.

1. In defense of our oculoplastic colleagues, we are not the only specialty referring patients to them for temporal artery biopsies. These referrals come from primary care, neurology, rheumatology for elderly patients with headache and PMR with low suspicion for GCA and low pre-test probability guided only by the theory of "stakes too high". In reality, the pre-test probability in patients without neuro-ophthalmic manifestations is very low. Just as we do not like seeing unnecessary referrals for blurred vision after cataract surgery in patients who have not refraction or haven't tried reading glasses, our oculoplastics colleagues don't like seeing low suspicion referrals for TAB. It limits access to patients who actually need to see them and may have something urgent like cancer.
2. In 2026, why would you not use evidence based medicine tools? We are neuro-ophthalmologists with big powerful brains, big powerful eyes, and big powerful tools. I think we can do better by our patients than using out dated aforisms to guide clinical care. If you truly subscribe to the "stakes too high" theory, you must recognize that TAB has less than 100% sensitivity, with estimates in the 30-70% range depending on the paper and in the seminal paper by Grant Liu and the Bascom Palmer group in 1994, 30% had vision better than 20/200 which made it look like NAION; are you getting MRIs and TAB on every presumed NAION and PET scans in cases of negative TAB just to make sure you never miss GCA? The scientific evidence and clinical practice simply does not match the logical conclusions of "stakes too high."

I find these evidence based tools invaluable on a regular basis. They are simple, easy to use, and add quantifiable value to our clinical suspicions and hunches.

Best,

Drew

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

For those of us in the real world the thought of missing Ta is catastrophic.  If we even suspect Ta as a possible diagnosis I get a biopsy. Period. If it's negative and I still have concerns clinically I treat as Ta and get a rheumatologist consult. Maybe all neuroophthalmologists should learn to do the biopsy. It's not difficult and it doesn't take much time.  Yes it pays nothing but it's a small price to pay for the privilege of practicing an amazing specialty and sub specialty. 

I think we could all benefit from a little compassion and modesty.

1. In defense of our oculoplastic colleagues, we are not the only specialty referring patients to them for temporal artery biopsies. These referrals come from primary care, neurology, rheumatology for elderly patients with headache and PMR with low suspicion for GCA and low pre-test probability guided only by the theory of "stakes too high". In reality, the pre-test probability in patients without neuro-ophthalmic manifestations is very low. Just as we do not like seeing unnecessary referrals for blurred vision after cataract surgery in patients who have not refraction or haven't tried reading glasses, our oculoplastics colleagues don't like seeing low suspicion referrals for TAB. It limits access to patients who actually need to see them and may have something urgent like cancer.
2. In 2026, why would you not use evidence based medicine tools? We are neuro-ophthalmologists with big powerful brains, big powerful eyes, and big powerful tools. I think we can do better by our patients than using out dated aforisms to guide clinical care. If you truly subscribe to the "stakes too high" theory, you must recognize that TAB has less than 100% sensitivity, with estimates in the 30-70% range depending on the paper and in the seminal paper by Grant Liu and the Bascom Palmer group in 1994, 30% had vision better than 20/200 which made it look like NAION; are you getting MRIs and TAB on every presumed NAION and PET scans in cases of negative TAB just to make sure you never miss GCA? The scientific evidence and clinical practice simply does not match the logical conclusions of "stakes too high."

I find these evidence based tools invaluable on a regular basis. They are simple, easy to use, and add quantifiable value to our clinical suspicions and hunches.

Best,

Drew

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

For those of us in the real world the thought of missing Ta is catastrophic.  If we even suspect Ta as a possible diagnosis I get a biopsy. Period. If it's negative and I still have concerns clinically I treat as Ta and get a rheumatologist consult. Maybe all neuroophthalmologists should learn to do the biopsy. It's not difficult and it doesn't take much time.  Yes it pays nothing but it's a small price to pay for the privilege of practicing an amazing specialty and sub specialty. 

I think we could all benefit from a little compassion and modesty.

1. In defense of our oculoplastic colleagues, we are not the only specialty referring patients to them for temporal artery biopsies. These referrals come from primary care, neurology, rheumatology for elderly patients with headache and PMR with low suspicion for GCA and low pre-test probability guided only by the theory of "stakes too high". In reality, the pre-test probability in patients without neuro-ophthalmic manifestations is very low. Just as we do not like seeing unnecessary referrals for blurred vision after cataract surgery in patients who have not refraction or haven't tried reading glasses, our oculoplastics colleagues don't like seeing low suspicion referrals for TAB. It limits access to patients who actually need to see them and may have something urgent like cancer.
2. In 2026, why would you not use evidence based medicine tools? We are neuro-ophthalmologists with big powerful brains, big powerful eyes, and big powerful tools. I think we can do better by our patients than using out dated aforisms to guide clinical care. If you truly subscribe to the "stakes too high" theory, you must recognize that TAB has less than 100% sensitivity, with estimates in the 30-70% range depending on the paper and in the seminal paper by Grant Liu and the Bascom Palmer group in 1994, 30% had vision better than 20/200 which made it look like NAION; are you getting MRIs and TAB on every presumed NAION and PET scans in cases of negative TAB just to make sure you never miss GCA? The scientific evidence and clinical practice simply does not match the logical conclusions of "stakes too high."

I find these evidence based tools invaluable on a regular basis. They are simple, easy to use, and add quantifiable value to our clinical suspicions and hunches.

Best,

Drew

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

For those of us in the real world the thought of missing Ta is catastrophic.  If we even suspect Ta as a possible diagnosis I get a biopsy. Period. If it's negative and I still have concerns clinically I treat as Ta and get a rheumatologist consult. Maybe all neuroophthalmologists should learn to do the biopsy. It's not difficult and it doesn't take much time.  Yes it pays nothing but it's a small price to pay for the privilege of practicing an amazing specialty and sub specialty. 

I think we could all benefit from a little compassion and modesty.

1. In defense of our oculoplastic colleagues, we are not the only specialty referring patients to them for temporal artery biopsies. These referrals come from primary care, neurology, rheumatology for elderly patients with headache and PMR with low suspicion for GCA and low pre-test probability guided only by the theory of "stakes too high". In reality, the pre-test probability in patients without neuro-ophthalmic manifestations is very low. Just as we do not like seeing unnecessary referrals for blurred vision after cataract surgery in patients who have not refraction or haven't tried reading glasses, our oculoplastics colleagues don't like seeing low suspicion referrals for TAB. It limits access to patients who actually need to see them and may have something urgent like cancer.
2. In 2026, why would you not use evidence based medicine tools? We are neuro-ophthalmologists with big powerful brains, big powerful eyes, and big powerful tools. I think we can do better by our patients than using out dated aforisms to guide clinical care. If you truly subscribe to the "stakes too high" theory, you must recognize that TAB has less than 100% sensitivity, with estimates in the 30-70% range depending on the paper and in the seminal paper by Grant Liu and the Bascom Palmer group in 1994, 30% had vision better than 20/200 which made it look like NAION; are you getting MRIs and TAB on every presumed NAION and PET scans in cases of negative TAB just to make sure you never miss GCA? The scientific evidence and clinical practice simply does not match the logical conclusions of "stakes too high."

I find these evidence based tools invaluable on a regular basis. They are simple, easy to use, and add quantifiable value to our clinical suspicions and hunches.

Best,

Drew

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value

For those of us in the real world the thought of missing Ta is catastrophic.  If we even suspect Ta as a possible diagnosis I get a biopsy. Period. If it's negative and I still have concerns clinically I treat as Ta and get a rheumatologist consult. Maybe all neuroophthalmologists should learn to do the biopsy. It's not difficult and it doesn't take much time.  Yes it pays nothing but it's a small price to pay for the privilege of practicing an amazing specialty and sub specialty. 

I think we could all benefit from a little compassion and modesty.

1. In defense of our oculoplastic colleagues, we are not the only specialty referring patients to them for temporal artery biopsies. These referrals come from primary care, neurology, rheumatology for elderly patients with headache and PMR with low suspicion for GCA and low pre-test probability guided only by the theory of "stakes too high". In reality, the pre-test probability in patients without neuro-ophthalmic manifestations is very low. Just as we do not like seeing unnecessary referrals for blurred vision after cataract surgery in patients who have not refraction or haven't tried reading glasses, our oculoplastics colleagues don't like seeing low suspicion referrals for TAB. It limits access to patients who actually need to see them and may have something urgent like cancer.
2. In 2026, why would you not use evidence based medicine tools? We are neuro-ophthalmologists with big powerful brains, big powerful eyes, and big powerful tools. I think we can do better by our patients than using out dated aforisms to guide clinical care. If you truly subscribe to the "stakes too high" theory, you must recognize that TAB has less than 100% sensitivity, with estimates in the 30-70% range depending on the paper and in the seminal paper by Grant Liu and the Bascom Palmer group in 1994, 30% had vision better than 20/200 which made it look like NAION; are you getting MRIs and TAB on every presumed NAION and PET scans in cases of negative TAB just to make sure you never miss GCA? The scientific evidence and clinical practice simply does not match the logical conclusions of "stakes too high."

I find these evidence based tools invaluable on a regular basis. They are simple, easy to use, and add quantifiable value to our clinical suspicions and hunches.

Best,

Drew

Hi all

Received this from our oculoplastics colleagues who do our TA biopsies. I am hoping to have some input as to how other institutions are approaching GCA workup 

some questions but any input is appreciated: 

• are others using these tools (mentioned below) to guide their decision to biopsy regardless of clinical suspicion and using these cutoffs to rule out or otherwise commit patient to treatment 
• are others relying more on TA ultrasound for diagnosis ? and if so who is doing the ultrasound (training for tech etc.) for this? 
• Would you not biopsy if ultrasound is negative but clinical suspicion is high ? 

Thank you ! 

Position Statement received: 

• Temporal artery biopsy (TAB) remains a useful diagnostic adjunct in selected patients with

  suspected giant cell arteritis (GCA). Our oculoplastic service is committed to providing timely

  access to this procedure for appropriate candidates. However, several clarifications are

  necessary:

  1. Our service is procedural. We do not specialize in the diagnosis or medical management

  of GCA, and we are not the only service capable of performing TAB. Our role is to

  perform the procedure when it is clinically appropriate, and we are not able to function as

  a default pathway for diagnostic uncertainty.

  2. TAB is an invasive surgical procedure with real risks, including bleeding, infection,

  nerve injury, and scarring. As with any diagnostic test, it should not be used

  reflexively or as a defensive measure in patients with low pretest probability, nor

  when results are unlikely to alter management

  3. There are well-validated clinical prediction models that improve patient selection for

  TAB. These tools help stratify patients into low-, intermediate-, and high-risk

  categories, guiding when biopsy is most likely to provide meaningful diagnostic

  value. Representative studies include Ing et al.1 Moudrous et al. 2 and subsequent

  validation work (Inayat et al., 2024). 3. "Using the Ing model, there were no positive

  biopsies below the threshold of 10.59% and no negative biopsies above the

  threshold of 68.44%. In this study population, this suggests that any patient with a

  score >68.44% could be presumed to have GCA without requiring TAB, whereas

  those with a score <10.59% can be presumed to not have GCA." 3

  The practical, validated tool is available here:

  https://edseling.com/giant-cell-arteritis-nomogram/

  Appropriate application of these models typically yields a positive biopsy rate of

  approximately 20–30%. Our current experience shows a positivity rate of only a few

  percent, strongly suggesting overutilization in low-probability patients.

  Updated Service Guidelines

  To align with evidence-based practice and responsible procedural use:

  ● We will perform TAB for patients with an estimated GCA probability of 10–70% using

  validated prediction tools, where biopsy is most likely to influence management.

  ● We will not perform TAB in patients outside this range as part of our service

  workflow:

  o <10% probability: low diagnostic yield; biopsy unlikely to impact care

  o >70% probability: treatment typically indicated regardless of biopsy result
• ● If there is suspicion for GCA, appropriate treatment with steroids should be initiated

  prior to referral for biopsy. Our service does not initiate or manage steroid treatment.

  This policy does not imply that biopsy is never appropriate outside these ranges. Rather,

  it defines the scope of procedures performed by our service. Any patients for whom

  biopsy is still desired outside (or of course within) these parameters may be referred to

  other services (e.g., general or vascular surgery).

  Conclusion

  We encourage referring providers to incorporate available risk stratification tools into

  their evaluation of suspected GCA. Our goal is to support appropriate, high-value care

  while avoiding unnecessary procedures for patients and unsustainable procedural

  burden on trainees. We remain available to perform TAB in appropriately selected

  patients and are happy to collaborate in this way on cases where clinical uncertainty

  exists.

  Abbreviated Reference list:

  Clin Ophthalmol. 2019 Feb 21;13:421–430. doi: 10.2147/OPTH.S193460

  Neural network and logistic regression diagnostic prediction models for giant cell

  arteritis: development and validation

  1. Edsel B Ing 1,✉, Neil R Miller 2, Angeline Nguyen 2, Wanhua Su 3, Lulu L C D

  Bursztyn 4, Meredith Poole 5, Vinay Kansal 6, Andrew Toren 7, Dana Albreki 8, Jack G

  Mouhanna 9, Alla Muladzanov 10, Mikaël Bernier 11, Mark Gans 10, Dongho Lee 12,

  Colten Wendel 13, Claire Sheldon 13, Marc Shields 14, Lorne Bellan 15, Matthew

  Lee-Wing 15, Yasaman Mohadjer 16, Navdeep Nijhawan 1, Felix Tyndel 17, Arun N E

  Sundaram 17, Martin W ten Hove 18, John J Chen 19, Amadeo R Rodriguez 20, Angela

  Hu 21, Nader Khalidi 21, Royce Ing 22, Samuel W K Wong 23, Nurhan Torun 24.

  PMCID: PMC6388759 PMID: 30863010

  2. Ann Med. 2022 Oct 21;54(1):2770–2776. doi: 10.1080/07853890.2022.2130971 A

  new prediction model for giant cell arteritis in patients with new onset headache

  and/or visual loss. Walid Moudrous

  a,b

  , Leo H Visser

  c,*

  , Tansel Yilmaz

  a

  , Marjan H

  Wieringa

  d

  , Tim Alleman

  e

  , Jörgen Rovers

  f

  , Mark PWA Houben

  g

  , Paula M Janssen

  b,g

  ,

  Johan J B Janssen

  h

  , Pieter L Rensma

  i

  , Geert J F Brekelmans

  c

  PMCID: PMC9601541

  PMID: 36269009

  3. Utility of online GCA risk models in predicting the result of temporal artery

  biopsy within a clinical setting: study of diagnostic and screening tests. Hamza

  Inayat *, Saerom Youn *, Lulu L.C.D. Bursztyn

  †

  ‡⁎

  . Schulich School of Medicine and

  Dentistry, Western University, London, Ont.

  †

  Department of Ophthalmology, Western

  University, London, Ont.

  ‡

  Clinical Neurological Sciences, Western University, London,

  Ont. Received 11 May 2023, Revised 23 October 2023, Accepted 20 November 2023,

  Available online 16 December 2023, Version of Record 17 September 2024.

  Addendum 1: Pretest Probability and Diagnostic Yield

  Pretest probability is the clinician's estimated likelihood that a patient has a given

  disease before diagnostic testing, based on clinical presentation, examination, and initial

  data. It is the key determinant of how informative a test result will be. This relationship is
• formalized by Bayes' theorem, which describes how a test result modifies disease

  probability. In practical terms, the post-test probability depends not only on the test's

  sensitivity and specificity, but also-critically-on the pretest probability.

  In low pretest probability settings, even tests with good performance characteristics

  produce a disproportionate number of false positives, resulting in low positive predictive

  value and limited clinical utility. In high pretest probability settings, a negative result may

  not meaningfully exclude disease, and management is often driven by clinical judgment

  rather than testing.

  Accordingly, diagnostic tests such as temporal artery biopsy provide the greatest value in

  intermediate-risk patients, where results are most likely to meaningfully shift

  management decisions. Applying TAB outside this range reduces diagnostic efficiency,

  increases unnecessary procedures, and exposes patients to risk without commensurate

  benefit.

  Bayes' Theorem

  P(A | B) = [P(B | A) · P(A)] / P(B)

  Definitions

  A, B = events

  P(A | B) = probability of A given that B is true

  P(B | A) = probability of B given that A is true

  P(A) = probability of A (prior probability)

  P(B) = probability of B

  For GCA:

  A = disease present (e.g., GCA)

  B = positive test (e.g., TAB positive)

  P(A) = pretest probability (from the GCA prediction tool or other methodology)

  P(B | A) = sensitivity

  P(A | B) = positive predictive value