Myasthenia Gravis - antibody tests

I have had problems with muscle weakness for several years.  A muscle biopsy showed abnormalities 7 years ago but the neurologists couldn't identify a specific disease.  A couple months ago I developed a choking sensation.  I was sent back to a major medical center, where several tests were done.  I was tested for the MUSK antibody, which was negative, but I was not tested for the Acetylcholine Receptor Antibody. The doctor said come back in six months and we'll see how you're doing, call if you get worse.

I didn't realize until I got home that I was not tested for both types of antibodies.  Are there reasons why a MUSK test only would be done?  Couldn't I have the Acetylcholine Receptor Antibody and not the MUSK?

Thank you for any insight into this.

[Abhijeet Deshmukh, MD]

Hello.

I wish you a very Happy new year.

The anti-AChR antibodies are found in about 80% of Myasthenia Gravis patients. This means that there is a large chunk of patients who are sero-negative.

The Muscle specific Tyrosine kinase (MuSK) antibodies are present in a significant number of the seronegative MG. Hence, this antibody test is done to confirm a seronegative MG.

You could have a positive Anti-AchR antibody result and negative anti-MuSK antibodies.

Regards