Palmaris brevis spasm syndrome.

Palmaris brevis spasm syndrome is a rare and benign condition of localised muscular hyperactivity. In five men, the hypothenar eminence underwent spontaneous, irregular, tonic contractions of the palmaris brevis muscle. An EMG showed spontaneous high frequency discharges of normal motor units, without evidence of neuropathy or of nerve compression. This syndrome resembles other restricted muscle hyperactivity syndromes although there are some differences. Curiously, the palmaris brevis muscle is not under voluntary control. The mechanism of the syndrome could be an ephaptic transmission possibly secondary to the transient and repeated stretching of the ulnar nerve superficial branch. In one patient a root compression was the probable origin.