The effect of dopamine replacement therapy on haptic sensitivity in Parkinson's disease

Increasing evidence indicates that processing of proprioceptive information is altered in Parkinson's disease (PD), leading to reduced kinaesthetic and haptic sensitivity. However, there is inconclusive evidence whether dopamine replacement therapy (DRT) ameliorates or worsens kinaesthetic and haptic function in PD. For assessing perceptual function, we employed a task that did not require active motion or stressed working memory function, which may become impaired in PD. A group of mild to moderate stage PD patients (n = 9) and a group of age-matched healthy controls participated in this study. Without vision, a subject's hand was moved by a robotic manipulandum along the contours of a small "virtual box" (5 x 15 cm). At the end of each trial, they indicated whether the contour was "curved" or "straight". PD patients were tested ON and OFF antiparkinsonian medication. Psychophysical detection thresholds were determined (curvature at which subjects correctly perceived a curved contour at the 75% level). Compared to the control group, thresholds were elevated by 55% in the PD patient group. During the ON medication state, the mean detection threshold of the patient group was reduced by 15% (ON: 4.71 m(-1); OFF: 5.42 m(-1)). Increases in curvature sensitivity were highly correlated with improved clinical scores of motor function (r = 0.74) with more affected patients showing higher gains in sensitivity as the result of DRT (r = 0.80). This report documents that DRT can ameliorate haptic and kinaesthetic function in patients with mild to moderate PD, suggesting that DRT can have beneficial effects on perceptual function.