[An elderly case of juvenile muscular atrophy in the unilateral upper extremity with tremor in both hands].

A 75-year-old man had noticed muscle atrophy and weakness of his right hand and forearm at the age of 25. The symptoms slowly progressed and then stopped. Right hand tremor appeared at about age 40. There was no symptom in his left upper extremity, and his gait was normal. He now shows severe muscle atrophy in his right hand and forearm. There was distally dominant weakness of the right upper extremity and his hand grip was 0 kg on the right and 25 kg on the left. On admission there was no weakness in the bilateral lower extremities. He had postural tremor in both hands and fingers. The tendon reflexes were hypoactive in the upper extremities and normal in the lower extremities. Abnormalities in the superficial sensation were unremarkable, whereas vibration sensation in both the upper and lower extremities was mildly disturbed. Electromyography revealed chronic denervation, especially in the right upper extremity. The sensory nerve conduction study results and somatosensory evoked potentials in the upper extremities were normal. Cervical MRI demonstrated spondylotic changes, canal stenosis from the C5 to C7 levels, and compression of the spinal cord. His hand tremor was dominant on the right with a peak frequency of about 7 Hz. Tremor frequency and power were decreased by mechanical load. Hirayama's disease (juvenile muscular atrophy of unilateral upper extremity) was the most probable diagnosis, although aging might have produced various additional abnormalities. The tremor seen in this patient showed characteristics of enhanced physiological tremor.