Joint position sense is impaired by Parkinson's disease

The abilities of Parkinson's disease (PD) patients, taking routine medicati on, and of control subjects, to discriminate bilateral differences in the s tatic angular positions of the two elbow joints were studied during passive (subject relaxed) and active (subject contracting to hold position) condit ions. On each trial, one of the subject's elbows served as the reference jo int (angle 60 degrees) and the other as the test joint (angular range, 54 d egrees to 63 degrees, at 3 degrees intervals). Subjects, with eyes closed, were required to discriminate the relative angles of the two elbows. In Exp eriments 1 (passive condition) and 2 (active condition), parkinsonians (n = 12) gave significantly fewer correct responses, pooled across sides, than did controls (n = 12), both in total scores across all angles and at indivi dual test angles of 57 degrees and 63 degrees. In Experiment 3 (passive con dition), derivation of conventional psychophysical variables indicated that both the difference limen (DL; threshold) and Weber ratio (WR; discriminat ory sensitivity, independent of absolute stimulus values; same as DL/PSE) v alues of patients (n = 6) were significantly larger than those of controls (n = 6), in the absence of a significant difference between groups in the p oint of subjective equality (PSE). Our results provide clear evidence of a quantitative impairment of joint position sense in PD patients.