Vestibular function and vestibulo-visual sensory integration in people with Parkinson’s disease: a comparison with age matched controls.

Abstract

Vestibular dysfunction may be a consequence of the neurodegenerative disorder, Parkinson’s disease (PD). Neuropathological studies support this hypothesis, but clinical studies of vestibular reflex testing have conflicting findings. Modern tests, the head impulse test (HIMP), the suppression head impulse test (SHIMP) and bone-conducted ocular and cervical vestibular-evoked myogenic potentials (oVEMPs and cVEMPs), have scarcely been reported in PD. Virtual reality (VR) assessment tools, have not been applied to PD. This prospective observational study compared vestibular function in 40 people with PD to 40 age-matched controls (HC). The study analysed dynamic vestibular reflex function: i) semi-circular canal mediated vestibulo-ocular reflex (VOR) and saccades with HIMP and SHIMP; ii) otolith mediated VOR with oVEMPs, and iii) otolith mediated vestibulo-collic reflex with cVEMPs. VEMPs were induced by both clicks and forehead taps. Static otolithic function was assessed via a VR subjective visual vertical (SVV) test. Vestibulo-visual integration was compared on a VR standing balance protocol. In early to mid-stage PD, VOR gains measured with HIMP and SHIMP were not significantly different from HC. However, in PD, SHIMP peak saccade velocity was reduced (p<.001) and latency prolonged (p=.003). Tap oVEMPs were more robust than clicks in both groups. PD had more absent cVEMP responses to both clicks (p=.03) and taps (p=.002) and more abnormal SVV responses (p=.01) with greater variability (p<.001). PD failed at lower levels of VR visual perturbation on both firm (p=.01) and foam surfaces (p=.001) than HC. Knowledge of vestibular dysfunction in PD will help guide targeted rehabilitation. From these findings, interventions for early to mid PD should focus on sensory integration protocols incorporating head motion.