Circulating antibodies of the acetylcholine receptor (AchRAb) are detectable in most patients with generalized myasthenia gravis (MG). A newly discovered antibody against muscle-specific kinase (MuSKAb) has been detected in 40-70% of AchRAb-negative MG patients. We report a series of Taiwanese MuSKAb-positive patients, and compare their clinical features with MuSKAb-negative patients and also with MuSKAb-positive Caucasians. Five out of 44 seronegative generalized MG patients (11.4%) were positive for MuSKAb. Patients with MuSKAb tended to have severe disability and bulbar involvement, and more often experienced crisis or impending crisis. Although all of these patients showed an initial response to immunosuppressant therapy, they had greater disability at follow-up. The clinical features of Taiwanese MuSKAb-positive patients were not different from those of Caucasians, except for a lower prevalence.
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