Evaluating the Effects of Levodopa on the Vestibulo-Ocular Reflex in Parkinson's Disease: A Case Series

Parkinson's disease (PD) is a neurodegenerative disorder primarily affecting individuals over 60 years old. The disorder is characterized by motor symptoms due in large part to the loss of dopamine-producing neurons. The vestibular system, crucial for maintaining balance, may be impacted in PD, contributing to balance issues through dysfunction in the vestibulo-ocular reflex. In this study, we aim to describe differences in vestibular responses before and after use of levodopa (L-DOPA) in patients with PD. The study evaluated nine PD patients who underwent videonystagmography, video head impulse testing, and rotational chair testing both on and off their dopaminergic medications. Effect sizes of the mean difference was measured using Cohen's d. The results revealed a general trend of increase in vestibular responses from the off stage to the on stage across all the vestibular testing mechanisms. The p values were all > .05, and the Cohen's d 95% confidence interval (CI) ranged from small to moderate effects with wide CIs consistent with the small sample. In this case series of nine patients with PD, we identified a general trend of a small increase in vestibular responses in the on state of L-DOPA compared with the off state of L-DOPA. The significance and clinical implications of such differences should be evaluated in larger samples.