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What Are The Symptoms Of Myasthenia Gravis?
Question: I just received my lab test back for Myasthenia Gravis Full Panel. What does it mean if only one of the test came back high? Here are my results.
Anti-Striation Abs was Negative
Achr Modulating Ab was normal at <12
Achr Blocking Abs, Serum was HIGH at 27
Achr Binding Abs, Serum was normal at <0.03
Anti-Striation Abs was Negative
Achr Modulating Ab was normal at <12
Achr Blocking Abs, Serum was HIGH at 27
Achr Binding Abs, Serum was normal at <0.03
Brief Answer:
Results not necessarily positive
Detailed Answer:
I read your question carefully and I understand your confusion.
It can happen that only one subtype of anticholine receptor antibody is abnormal in Myasthenia Gravis (MG). Had it been the binding antibodies which were positive, the commonly positive ones, I would have said that the test was indicative for MG even if the others were normal, as that often is the case.
However in your case it's the blocking antibodies. These antibodies are almost never positive alone, they usually accompany the rise of other antibodies.
The figure itself is not clear cut because usually positive is considered above 42%, while from 26 to 41% is considered indeterminate. Therefore 27% would be at the border of negative and indeterminate, not considered positive. They should be correlated with reference ranges in your lab though.
So bottom line, those values are not that meaningful because they are not high enough to be considered positive and they are not associated with high values of other antibodies as they usually are.
That doesn't mean that MG is excluded though, there are other antibodies like anti MuSK which should be tested for. Even if they come back negative there are rare cases where no known antibodies are found in the presence of the disease, antibodies support the diagnosis, not exclude it.
So the interpretation of the results is made together with the clinical data and results of EMG testing, if they strongly indicate MG the diagnosis is made even without any positive antibody.
I remain at your disposal for further questions.
Results not necessarily positive
Detailed Answer:
I read your question carefully and I understand your confusion.
It can happen that only one subtype of anticholine receptor antibody is abnormal in Myasthenia Gravis (MG). Had it been the binding antibodies which were positive, the commonly positive ones, I would have said that the test was indicative for MG even if the others were normal, as that often is the case.
However in your case it's the blocking antibodies. These antibodies are almost never positive alone, they usually accompany the rise of other antibodies.
The figure itself is not clear cut because usually positive is considered above 42%, while from 26 to 41% is considered indeterminate. Therefore 27% would be at the border of negative and indeterminate, not considered positive. They should be correlated with reference ranges in your lab though.
So bottom line, those values are not that meaningful because they are not high enough to be considered positive and they are not associated with high values of other antibodies as they usually are.
That doesn't mean that MG is excluded though, there are other antibodies like anti MuSK which should be tested for. Even if they come back negative there are rare cases where no known antibodies are found in the presence of the disease, antibodies support the diagnosis, not exclude it.
So the interpretation of the results is made together with the clinical data and results of EMG testing, if they strongly indicate MG the diagnosis is made even without any positive antibody.
I remain at your disposal for further questions.
Above answer was peer-reviewed by :
Dr. Chakravarthy Mazumdar
Thank you. I do have a few more questions. Is there anything else that would make the blocking antibodies at 27? Another type of disease? I have been formally diagnosed with fibromyalgia for about 8 years. My eye doc sent me to neuro because he suspected MG due to drooping eye lid. Could my IBS medicine cause blocking antibodies? I don't take on a regular basis and only take one if my stomach is hurting so average about 3 pills a month but I think I took one the day of the test. It is Dicyclomine. Consequently I am now now prednisone for sinus infection and I have felt much better as far as fatigue and muscles aches so I am thinking maybe something autoimmune is going on, if not MG, then something else? What would be your assessment?
Brief Answer:
Read below
Detailed Answer:
Thank you for that update.
Regarding what medication could affect the values, no, your IBS medication does not affect antibody titers, the only medication which can is penicillamine (used usually in rheumatoid arthritis).
The titers can be elevated in other autoimmune conditions like some paraneoplastic syndromes and rheumatological conditions, but that is very very rare, they are pretty specific for myasthenia.
However as I said, before going into discussions about what causes positivity, remember that I told you that 27% is not positive, it's indeterminate, and only 1% more than negative. Honestly that might be a reason to repeat the test at most, but certainly can't be considered positive.
As for your history, fatigue and muscle ache might well be in the setting of fibromyalgia if other rheumatological disorders have been excluded. Drooping eyelid (ptosis) is not typical though, so in front of a combination of fatigue and ptosis myasthenia is a diagnosis to be carefully evaluated, your doctor is right about that.
Prednisone would improve myasthenia but it usually takes some weeks/months to do so. However your assessment for myasthenia is not complete without electrodiagnostic studies, considering the ptosis I believe them to be necessary as well as a test called edrophonium test (administration of edrophonium which should promptly improve your symptoms).
As for other causes as you suggested they could be autoimmune conditions like polymiositis, thyroid disorders, hepatitis C. However I suspect tests for those (erythrosedimentation rate, c reactive protein, thyroid function, liver tests creatine kinase etc) must have already been done since they are usually part of evaluation for fibromyalgia (fibromyalgia is a diagnosis of exclusion, so these test should be normal before diagnosing fibromyalgia), so they might have already been excluded by your doctor.
I hope to have been of help.
Read below
Detailed Answer:
Thank you for that update.
Regarding what medication could affect the values, no, your IBS medication does not affect antibody titers, the only medication which can is penicillamine (used usually in rheumatoid arthritis).
The titers can be elevated in other autoimmune conditions like some paraneoplastic syndromes and rheumatological conditions, but that is very very rare, they are pretty specific for myasthenia.
However as I said, before going into discussions about what causes positivity, remember that I told you that 27% is not positive, it's indeterminate, and only 1% more than negative. Honestly that might be a reason to repeat the test at most, but certainly can't be considered positive.
As for your history, fatigue and muscle ache might well be in the setting of fibromyalgia if other rheumatological disorders have been excluded. Drooping eyelid (ptosis) is not typical though, so in front of a combination of fatigue and ptosis myasthenia is a diagnosis to be carefully evaluated, your doctor is right about that.
Prednisone would improve myasthenia but it usually takes some weeks/months to do so. However your assessment for myasthenia is not complete without electrodiagnostic studies, considering the ptosis I believe them to be necessary as well as a test called edrophonium test (administration of edrophonium which should promptly improve your symptoms).
As for other causes as you suggested they could be autoimmune conditions like polymiositis, thyroid disorders, hepatitis C. However I suspect tests for those (erythrosedimentation rate, c reactive protein, thyroid function, liver tests creatine kinase etc) must have already been done since they are usually part of evaluation for fibromyalgia (fibromyalgia is a diagnosis of exclusion, so these test should be normal before diagnosing fibromyalgia), so they might have already been excluded by your doctor.
I hope to have been of help.
Above answer was peer-reviewed by :
Dr. Chakravarthy Mazumdar
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