LEVODOPA REDUCES MUSCLE TONE AND LOWER-EXTREMITY TREMOR IN PARKINSONS-DISEASE

Objective: We have quantified the effects of levodopa treatment in Par kinsonian subjects during maintained stance. Methods: Electromyographi c muscle activity during quiet stance was assessed in subjects with Pa rkinson's disease, who exhibited a fluctuating response to levodopa, a nd in age-matched control subjects. Stance stability was also assessed from mean displacement and velocity of the center of pressure excursi ons during stance, Results: Lower extremity and trunk muscles showed h igh amplitude activity in all Parkinson's subjects when ''off', and a 4-5 Hz tremor in three of these subjects, When ''on'', the amplitude o f muscle activity was reduced in the distal muscles more than the prox imal, while tremor was suppressed in all muscles, Corresponding to the excessive muscle activity, the Parkinson's subjects had increased vel ocity and variability of velocity in the anterior-posterior center of foot pressure excursions, but the mean displacement of the center of p ressure excursion was not different from the controls. The velocity of center of pressure excursions in the Parkinson's subjects ''on'', app roached those of the control subjects suggesting that the excessive di stal muscle amplitude and tremor contributed to the high velocity of t he center of pressure. Conclusions: These findings suggest that dopami nergic systems are involved in the regulation of muscle tone during st ance, Depletion of dopaminergic transmission results in increased musc le tone and tremor in the lower extremities which may contribute to ch anges in posture and stability.