Enhancement of rigidity in Parkinson's disease with activation

Rigidity, a cardinal symptom of Parkinson's disease (PD), increases with movement of a contralateral limb. It is unclear whether this effect is specific for movement of a contralateral limb. The goal of this study was to test the hypothesis that ipsilateral or contralateral movement would enhance rigidity but that bilateral limb movements would maximally increase rigidity in people with PD. We assessed rigidity in 12 people with PD off meds, 12 matched controls, and 10 young controls, using a Rigidity Analyzer (Neurokinetics, Alberta, Canada). The elbow was passively moved repetitively into flexion and extension by the examiner, while the subjects engaged in different toe tapping conditions: no tapping, ipsilateral tapping, contralateral tapping, and bilateral tapping. Three 50-second trials were done for each condition and the order of the trials was randomized. A 2-way repeated measures ANOVA and Holm-Sidak post hoc tests were used to determine differences across conditions and groups. There was a significant effect of group, tapping conditions and an interaction of the two. Post hoc tests revealed that for the PD group, all tapping conditions were significantly different from the no tapping condition but not different from each other. There were no differences across conditions for the controls. We conclude that movement of either the contralateral or ipsilateral lower extremity can increase arm rigidity in people with PD but the effects from left and right are apparently not additive. Further, activation did not enhance muscle tone in controls suggesting that this procedure may help distinguish people with PD from controls.