[Juvenile asymmetrical segmental spinal muscular atrophy].

We report the case of a man who had an insidious onset of asymmetrical distal muscle weakness of the upper extremity at the age of 17. Objective findings were 1) muscular atrophy of calf and forearm flexor muscles and intrinsic hand muscles; 2) fasciculations; and 3) hand tremor. EMG and muscle biopsy showed neurogenic changes. MRI of the medulla and plasma creatine kinase were normal. Genetic testing for SMA-III was negative.