Continuous muscle activity and distal spinal muscular atrophy.

A young man presented with myokymias, cramp-like difficulty in muscle relaxation and peroneal atrophy. EMG studies revealed continuous muscle activity (CMA) manifested as grouped potentials and high frequency discharges. Sensory nerve conduction studies and sural nerve biopsy gave normal results, and he was thought to suffer from distal spinal muscular atrophy with CMA. This association suggests that the lower motor neuron may have an important role in the generation of the continuous muscle activity.