Cortical myoclonus in levodopa-responsive parkinsonism.

We observed myoclonic movements of the fingers and wrists in two patients with a levodopa-responsive parkinsonian syndrome most consistent with Parkinson's disease. These patients were studied with electrophysiological techniques. Brief (<50 ms) myoclonic electromyographic discharges showed a time-locked relationship to a focal premovement electroencephalographic potential. Somatosensory-evoked potentials were not enlarged and long-latency reflexes were not grossly exaggerated. This pattern of electrophysiological findings can be distinguished from those previously found in other parkinsonian syndromes. These results provide evidence for a cortical origin of the myoclonus seen in these patients.