Myasthenia gravis, MuSK antibody positive (Q88643)

Approximately 50% of the Acetylcholine receptor-negative patients have autoantibodies against muscle-specific kinase (MuSK). MuSK MG is a separate disease entity given the characteristic pattern of weakness, disease course and pathophysiology. MuSK MG is 20 x as rare as AChR –positive MG (prevalence 1–2 per 10,000 persons). Most patients are female, have an onset <40 years, present with ptosis and diplopia, may rapidly develop bulbar weakness (oculobulbar presentation) and are at higher risk of respiratory crisis. One-third to half of MuSK MG patients may experience myasthenic crises requiring ventilatory support. Limb muscle weakness is less severe. Small thymomas have occasionally been reported.