Anti-MuSK Antibody-positive Myasthenia Gravis Mimicking Amyotrophic Lateral Sclerosis.

We herein investigated the clinical features of three patients with anti-muscle-specific tyrosine kinase (MuSK) antibody-positive myasthenia gravis (MG), which was initially difficult to distinguish from amyotrophic lateral sclerosis (ALS). The patients exhibited dropped head syndrome or dysphagia as initial symptoms. Although their clinical findings were compatible with the revised El Escorial Criteria for ALS, their progression appeared to be more rapid than that of ALS. Both the edrophonium and repetitive nerve stimulation tests yielded negative results, and diurnal fluctuation was not confirmed. The patients were ultimately diagnosed with anti-MuSK antibody-positive MG. We therefore recommend the measurement of anti-MuSK antibodies when encountering such cases.