Muscle silent period in Parkinson's disease.

The muscle silent period was measured in 11 patients with moderate to severe rigidity associated with Parkinson's disease. The determinations were made under conditions of maximum disability for each patient, since all medications had been withdrawn before testing. The duration of the EMG silence, produced by small and large electrical twitch contractions of the adductor pollicis muscle, fell within a range of values previously determined for normal individuals. Major alleviation of the rigidity and bradykinesia with chronic oral l-dopa therapy was not accompanied by any change in the silent period. It was concluded that in untreated Parkinsonism, and also after its treatment with l-dopa, the functioning of the muscle spindles and local inhibitory reflexes remains normal.