NANOSNET

Mitch,

What do you mean by "screening" test? Typically a screening test in done in a certain population of patients to look for a disease, ideally it has high sensitivity to rule out disease.

Applying this concept of "screening" to OMG would suggest testing all patients with double vision or ptosis. Given the low prevalence and also low sensitivity (ACHR binding antibodies are ~50-60%, Musk is about 5%, ACHR modulating ~5% (1/7th of bind negative), ACHR blocking minimal, LRP4 ~4% (10% of double neg)). None of these tests are individually suitable for screening and should only be ordered in patients in which there is a high pre-test probability based on clinical suspicion for myasthenia.

In the setting of a patient with high clinical suspicion for OMG, ACHR binding antibodies make the most sense as the first test. The rest of the tests add limited utility (high false negatives and unlikely to be positive, further positive tests are unlikely to change management in a patient with clear clinical manifestations such as variable / intermittent symptoms with fatigability on exam) with significant cost. They also add to patient testing fast and erode trust in the physician.

If there is clinical doubt of diagnosis in the setting of negative ACHR binding antibodies, single-fiber EMG with repetitive nerve stimulation has the next best sensitive and specificity although the sensitivity is lower than in generalized MG (as are all the antibodies).

If sf-EMG isn't available , probably next best bet is monitoring for variability every 2-4 weeks. We did show a 70% response wait to prednisone 10 mg after 1 month so you could consider a treatment trial but would want to wait at least 3-4 months in a double vision patient to make sure any improvement isn't from typical recovery of a microvascular nerve palsy.

I do love the Mayo lab, they do great work, and the concept of reflex testing makes a lot sense from a cost saving perspective. However, if many commercial labs won't send out to them and if you order the test to be drawn at a University facility and send out often the University facility pays the bill, not the insurance or patient. In the modern economic atmosphere affecting many University health care systems, this is not a good use of resources.

The toughest questions I think are how sure do you have to be before doing eyelid or strabismus surgery.

Best, 

Drew

Mitch,

What do you mean by "screening" test? Typically a screening test in done in a certain population of patients to look for a disease, ideally it has high sensitivity to rule out disease.

Applying this concept of "screening" to OMG would suggest testing all patients with double vision or ptosis. Given the low prevalence and also low sensitivity (ACHR binding antibodies are ~50-60%, Musk is about 5%, ACHR modulating ~5% (1/7th of bind negative), ACHR blocking minimal, LRP4 ~4% (10% of double neg)). None of these tests are individually suitable for screening and should only be ordered in patients in which there is a high pre-test probability based on clinical suspicion for myasthenia.

In the setting of a patient with high clinical suspicion for OMG, ACHR binding antibodies make the most sense as the first test. The rest of the tests add limited utility (high false negatives and unlikely to be positive, further positive tests are unlikely to change management in a patient with clear clinical manifestations such as variable / intermittent symptoms with fatigability on exam) with significant cost. They also add to patient testing fast and erode trust in the physician.

If there is clinical doubt of diagnosis in the setting of negative ACHR binding antibodies, single-fiber EMG with repetitive nerve stimulation has the next best sensitive and specificity although the sensitivity is lower than in generalized MG (as are all the antibodies).

If sf-EMG isn't available , probably next best bet is monitoring for variability every 2-4 weeks. We did show a 70% response wait to prednisone 10 mg after 1 month so you could consider a treatment trial but would want to wait at least 3-4 months in a double vision patient to make sure any improvement isn't from typical recovery of a microvascular nerve palsy.

I do love the Mayo lab, they do great work, and the concept of reflex testing makes a lot sense from a cost saving perspective. However, if many commercial labs won't send out to them and if you order the test to be drawn at a University facility and send out often the University facility pays the bill, not the insurance or patient. In the modern economic atmosphere affecting many University health care systems, this is not a good use of resources.

The toughest questions I think are how sure do you have to be before doing eyelid or strabismus surgery.

Best, 

Drew

Mitch,

What do you mean by "screening" test? Typically a screening test in done in a certain population of patients to look for a disease, ideally it has high sensitivity to rule out disease.

Applying this concept of "screening" to OMG would suggest testing all patients with double vision or ptosis. Given the low prevalence and also low sensitivity (ACHR binding antibodies are ~50-60%, Musk is about 5%, ACHR modulating ~5% (1/7th of bind negative), ACHR blocking minimal, LRP4 ~4% (10% of double neg)). None of these tests are individually suitable for screening and should only be ordered in patients in which there is a high pre-test probability based on clinical suspicion for myasthenia.

In the setting of a patient with high clinical suspicion for OMG, ACHR binding antibodies make the most sense as the first test. The rest of the tests add limited utility (high false negatives and unlikely to be positive, further positive tests are unlikely to change management in a patient with clear clinical manifestations such as variable / intermittent symptoms with fatigability on exam) with significant cost. They also add to patient testing fast and erode trust in the physician.

If there is clinical doubt of diagnosis in the setting of negative ACHR binding antibodies, single-fiber EMG with repetitive nerve stimulation has the next best sensitive and specificity although the sensitivity is lower than in generalized MG (as are all the antibodies).

If sf-EMG isn't available , probably next best bet is monitoring for variability every 2-4 weeks. We did show a 70% response wait to prednisone 10 mg after 1 month so you could consider a treatment trial but would want to wait at least 3-4 months in a double vision patient to make sure any improvement isn't from typical recovery of a microvascular nerve palsy.

I do love the Mayo lab, they do great work, and the concept of reflex testing makes a lot sense from a cost saving perspective. However, if many commercial labs won't send out to them and if you order the test to be drawn at a University facility and send out often the University facility pays the bill, not the insurance or patient. In the modern economic atmosphere affecting many University health care systems, this is not a good use of resources.

The toughest questions I think are how sure do you have to be before doing eyelid or strabismus surgery.

Best, 

Drew