CLINICAL CORRELATES OF MOTOR-PERFORMANCE DURING PACED POSTURAL TASKS IN PARKINSONS-DISEASE

Bradykinesia and hypokinesia may both play a significant role in postu ral instability commonly seen in patients with Parkinson's disease. We investigated which factor -movement time or movement amplitude -is th e more significant limiting variable in patients with Parkinson's dise ase during a paced postural task. We also assessed the effect of antip arkinson medication upon these movement factors and the degree of corr elation with changes in clinical performance. Subjects performed paced left-right (L-R) and forward-backward (F-B) continuous weight-shiftin g tasks at slow, medium and fast paces. Ten Parkinson patients were st udied both OFF and ON their usual antiparkinson medication. Ten age-ma tched healthy controls were also tested and subsequently retested on t he same schedule as the patients. Movement times and amplitudes were m easured and correlated with clinical changes in UPDRS motor subscores. Parkinson patients performed similar to controls with respect to move ment time, but significantly displayed underscaled (reduced) movement amplitude. Movement amplitude improved after antiparkinson medication, but remained significantly less than that of controls. Improvements i n L-R movement amplitude correlated with clinical improvements in brad ykinesia and postural instability, while improved F-B movement amplitu de correlated only with reduced postural instability. We conclude that hypometric movement amplitude, and not abnormal movement time, is the primary abnormality observed in Parkinson patients during a paced pos tural task. Amplitude underscaling seems antiparkinson medication-depe ndent and improvement correlates with favorable clinical changes in br adykinesia and postural instability scores.