A Case of Anti-MuSK Antibody-positive Myasthenia Gravis That Was Diagnosed After Appearance of Dysphagia

Myasthenia gravis (MG) is an autoimmune disorder in which receptors at the neuromuscular junctions are destroyed by autoantibodies. The typical autoantibodies associated with MG include acetylcholine receptor (AChR) antibody and muscle-specific receptor (MuSK) antibody. MuSK antibody-positive MG (MuSK-MG) accounts for approximately 5% of all cases of MG and the primary symptom is bulbar palsy. On the other hand, ocular symptoms are rare in the early stage of the disease. In this case, we encountered a patient who complained of pharyngeal dysphoria and diplopia of unknown origin. She was diagnosed as having MuSK-MG after the emergence of dysphagia during follow-up. Because the bulbar palsy in MuSK-MG is often progressive, we believe that the involvement of an otolaryngologist is important for the diagnosis and assessment of patients with MuSK-MG.