Effect of L-dopa Medication on Postural Control in Parkinson's Disease: A Posturographic Study

ABSTRACT

BACKGROUND: The purpose of this study was to investigate abnormalities of postural control in Parkinson's disease (PD) patients during unperturbed stances and externally perturbed stances, and also to assess the effects of L-dopa medication on posture control. METHODS: Thirty PD patients were compared with 30 normal controls. Subjects' spontaneous sway during an unperturbed stance and the postural responses to anterior-posterior tilts of the support surface and of the visual scene were measured by posturography. RESULTS: During the unperturbed stance, displacement, velocity and frequency of the center of foot pressure (COP) were abnormally large in patients OFF treatment. Under L-dopa treatment, the velocity and frequency of COP and axial stiffness of PD patients were reduced, whereas sway amplitude increased. A frequency peak in the COP excursions at 0.7-1.1 Hz, which indicates a resonance behavior of the postural control loop, became reduced under therapy. Abnormal postural responses to tilting of the platform showed that the righting response of the upper body on the lower body was impaired in the PD patients. The postural responses of the PD patients to visual tilt was abnormally exaggerated and not dependent on the stability of the platform unlike the control subjects. These abnormal tilt reactions of the PD patients were resistant to treatment with L-dopa. CONCLUSIONS: These findings suggest that postural instability in PD is more critically related to high sway velocity and frequency than sway amplitude. The patients with PD are short of the ability to use the proprioceptive and visual information for the postural righting response when perturbed.