Levodopa-induced dyskinesia alters postural control in people with Parkinson's disease.

While levodopa is the most effective drug for symptom treatment of Parkinson's Disease (PD), its long-term use often leads to side effects such as uncontrolled involuntary movements known as levodopa-induced dyskinesia (LID). LID has been shown to increase postural sway, but the extent to which these hyperkinetic movements alter postural sway strategies has not been explored. We recruited 25 people with idiopathic PD, of which 13 exhibit clinical signs of LID, and 10 healthy older adults. Participants performed thirty-second standing trials with no added task (single-task) and with performing a cognitive dual-task, known to provoke dyskinesia. Participants with PD were tested in their practical OFF and ON states. The root-means-square (RMS) accelerations were obtained from inertial sensors attached to the lumbar, trunk, and head. Sway ratios (superior-to-inferior segment) were calculated to determine the effect of LID on postural sway strategies. Participants with LID showed greater RMS head sway, compared to those without LID and older adults. The head-to-trunk sway ratio was greater in participants with LID during the ON state or when dual-tasking. In addition, the head-to-lumbar sway ratio was greater in participants with LID in the ON state during both single- and dual-tasking. Our results reveal an altered postural control strategy in PD with LID, presenting increased sway in superior segments of the kinematic chain, leading to head instability. Unlike PD without LID and older adults, PD with LID exhibit multi-link sway in the ON state, which has important implications for measuring postural sway in the presence of dyskinesias.