Essential myoclonus: report of four cases.

Four cases of essential myoclonus in childhood are reported. These include three males and one female, whose age-at-onset ranged from 2 months to 16 years. All manifested as involuntary movement of face, neck, or extremities without any known etiology. Only one case has a family history of myoclonus. They showed no other neurological abnormalities. The image or electrophysiological studies of nervous systems were within normal limits except that electromyogram (EMG) showed myoclonic discharge. All were treated by clonazepam with or without valproic acid. No significant effects were noted.