Levodopa Reduces Muscle Tone and Lower Extremity Tremor in
Parkinson's Disease
Levodopa Reduces Muscle Tone and Lower Extremity Tremor in
Parkinson's Disease
Abstract:
Objective: We have quantified the effects
of levodopa treatment in Parkinsonian subjects during maintained
stance. Methods: Electromyographic muscle activity
during quiet stance was assessed in subjects with Parkinson's
disease, who exhibited a fluctuating response to levodopa, and
in age-matched control subjects. Stance stability was also assessed
from mean displacement and velocity of the center of pressure
excursions during stance. Results: Lower extremity
and trunk muscles showed high amplitude activity in all Parkinson's
subjects when "off", and a 4-5 Hz tremor in three of these subjects.
When "on", the amplitude of muscle activity was reduced in the
distal muscles more than the proximal, while tremor was suppressed
in all muscles. Corresponding to the excessive muscle activity,
the Parkinson's subjects had increased velocity and variability
of velocity in the anterior-posterior center of foot pressure
excursions, but the mean displacement of the center of pressure
excursion was not different from the controls. The velocity
of center of pressure excursions in the Parkinson's subjects
"on", approached those of the control subjects suggesting that
the excessive distal muscle amplitude and tremor contributed
to the high velocity of the center of pressure. Conclusions:
These findings suggest that dopaminergic systems are involved
in the regulation of muscle tone during stance. Depletion of
dopaminergic transmission results in increased muscle tone and
tremor in the lower extremities which may contribute to changes
in posture and stability.
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Can.
J. Neurol. Sci. 1995; 22: 280-285
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