Objective: We tested if the administration of levodopa leads the patients with Parkinson’s disease to sway significantly more than the controls, especially under challenging visual tasks, and if (because) levodopa does not adjust the contribution of postural control mechanisms and body segment rotations to perform these tasks.

Background: Patients with Parkinson’s disease off-drug exhibited altered postural control under active visual tasks, i.e. they turned their full body in-block instead of their head (Bonnet et al., 2015). Moreover, the patients off-drug did not seem able to adjust their postural control mechanisms in gaze shift tasks (Bonnet et al., 2015). Several published manuscripts additionally showed that levodopa did not clearly improve postural control and the way the body segments moved.

Methods: Fourteen patients (65±6 years; Hoehn and Yahr stage: 2±0.5; UPDRS motor score off-drug: 27±5) and 14 controls performed three visual tasks (3 trials per task, 32 sec per trial). They looked at a stationary dot or they gazed at a dot appearing alternatively left and right at 80° of visual angle, either at 0.125 Hz or at 0.25 Hz. The patients were off-drug and then on-drug and the controls were off-drug twice.

Results: The patients on-drug swayed significantly more than the controls in the three tasks. The levodopa treatment did not improve body segment rotations but it led the patients to increase the contribution of their postural mechanisms signifcantly more than the controls (in absolute terms). However, in relative terms, the patients did not increase the contribution of their mechanisms enough to control their upright stance, potentially explaining why they swayed more than the controls. Most problematically, the patients moved their lower back significantly faster than the controls.

Conclusions: The results showed that under on-drug conditions, the patients with Parkinson’s disease are engaged to sway significantly more than controls even if they definitely increase the contribution of their postural mechanisms. Hence, the patients on-drug use more energy to control their upright stance but are still less efficient than healthy adults, especially in challenging active tasks. Most problematically, the patients moved significantly more their lower-back than the controls, especially on-drug, and this strategy may be the most important cause of falls and hip fractures (Rogers & Mille, 2003).

References: Bonnet CT, Delval A, Defebvre L. Parkinson’s disease-related impairments in body movement, coordination and postural control mechanisms when performing 80° lateral gaze shifts. IEEE Trans. Neural. Syst. Rehabil. Eng. 2015;23:849-856.

Rogers MW, Mille M-L. Lateral Stability and Falls in Older People. Exercise Sport Sci. R. 2003;31:182-187.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/effects-of-the-administration-of-levodopa-on-postural-control-under-visual-tasks/