A clinical and electrophysiological evaluation of myoclonus.

The records of 23 consecutive patients with myoclonus who were seen during a 16-month period were analyzed prospectively. The patients were divided into two groups: epileptic and nonepileptic. The epileptic patients had focal and stimulus-elicitable myoclonus with enlarged somatosensory evoked potentials and enhanced long-loop reflexes, and they responded well to anticonvulsants, especially clonazepam and valproic acid. The nonepileptic group had massive and spontaneous jerks with normal-sized somatosensory evoked potentials and long-loop reflexes, and they responded poorly to anticonvulsants. Evaluation of these clinical and electrophysiologic characteristics can help in the classification of obscure movement disorders and in predicting responses to therapy.