15~20% of patients with myasthenia gravis who have no anti-acetylcholine receptor (AchR) antibody
have antibodies to muscle specific tyrosine kinase (MuSK) and about 5% have neither anti-AchR
nor anti-MuSK antibodies. Exact understandings of their clinical manifestations and action mechanisms
of antibodies have been still unclear. Detection of anti-MuSK antibody defines a rare form of
myasthenia gravis, but it may be difficult to diagnose. An improved antibody-detection assay would be
helpful in patients without AchR or MuSK antibodies. The conventional therapy may not respond well
to patients who have this antibody. So, it can be life threatening and may require additional treatments.
We review recent studies on anti-MuSK antibody associated with myasthenia gravis, and summarize
the results of new management of myasthenia gravis.

KEYWORDS : Antibody, Muscle specific tyrosine kinase, Myasthenia gravis, Seronegativ