A case of bulbospinal muscular atrophy with large fasciculation manifesting as spinal myoclonus

OBJECTIVE: This paper reports a patient with bulbospinal muscular atrophy (BSMA) who presented with spinal myoclonus, documented by video and surface electromyography. CASE REPORT: A 66-year-old man had progressive gait disturbance, dysphagia, and easy fatigability of all extremities over a period of 4 years. Neurologically, muscle atrophy, fasciculation, and weakness were observed in the bulbar and limb muscles. When the knees were kept in mild flexion in the supine position, fasciculation of the thigh adductor muscles was so large that it caused shock-like involuntary movements of the legs, corresponding to spinal myoclonus. A genetic test revealed 41 repeats of CAG in the androgen receptor gene, and the diagnosis of BSMA was made. SIGNIFICANCE: The present case suggests that extremely large fasciculation can cause spinal myoclonus.