X-linked spinal and bulbar muscular atrophy with myasthenic symptoms.

We describe a patient with X-linked spinal and bulbar muscular atrophy (X-SBMA) and myasthenic symptoms. The diagnosis of X-SBMA was established by demonstration of the increased number of CAG repeats in the androgen receptor gene on the X chromosome. This patient was characterized by the clinical symptoms of fatigability, decremental motor responses to repetitive nerve stimulation, and improvement of the myasthenic symptoms with oral administration of pyridostigmine. No serum antibody to acetylcholine receptor was detected. It is suggested that, in the process of chronic denervation and reinnervation of X-SBMA, reinnervated motor endplates may be associated with the defect of neuromuscular transmission.