Generalized Myasthenia Gravis with Anti-acetylcholine Receptor Antibodies during the Clinical Course of Spinal and Bulbar Muscular Atrophy: A Case Report

A 44-year-old man with spinal and bulbar muscular atrophy (SBMA) and an anterior mediastinal tumor presented with ptosis and diplopia with diurnal variation. Dysarthria, dysphagia, and limb weakness deteriorated acutely, and developed respiratory failure. Repetitive nerve stimulation resulted in a decremental response. Ice pack and edrophonium tests were positive. Myasthenia gravis (MG) was diagnosed based on the presence of anti-acetylcholine receptor (AChR) antibodies. Immunotherapy improved the myasthenic symptoms. Although a few cases of SBMA exhibiting myasthenic symptoms have been reported, none of these patients had anti-AChR antibodies. This is the first report of seropositive MG with comorbid SBMA.