Infantile onset myasthenia gravis with MuSK antibodies

Abstract

Approximately 80% of patients with myasthenia gravis (MG) show a high antibody (Ab) titer against acetylcholine receptor (AChR). Patients with MG who do not have high titer of anti-AChR are called seronegative MG (SNMG) and their clinical characteristics are shown to be rather different from anti-AChR positive MG in the literature.1 It was recently reported that 70% of sera from generalized SNMG patients contained Ab to a muscle-specific receptor tyrosine kinase (MuSK).2 The frequency of anti-MuSK Ab in generalized SNMG is reportedly from 38% to 47% of cases.3–5 Anti-MuSK MG mainly affects young to middle-aged adults. We describe a case of late infantile onset MG with anti-MuSK Ab. A 29-year-old man first experienced bilateral ptosis after febrile seizures when he was 2 years old. His parents soon noticed abnormal phonation. At age 3 years, the diagnosis of MG was made based on a positive edrophonium test. Treatment was initiated with oral prednisolone. His ocular symptoms responded well to …