(PP1508) Vestibular Perceptual Thresholds in Chronic Vestibular Disorders

Persistent postural-perceptual dizziness (PPPD) currently presents a diagnostic challenge as traditional vestibular assessments fail to identify specific abnormalities. As these assays assess reflexive pathways and not perception, these may be insensitive as changes in perception and integration of vestibular input have been proposed to underlie PPPD. This study assessed vestibular perceptual thresholds in patients with PPPD and healthy controls, to for the first time, directly characterize vestibular perception in this patient population. Patients with PPPD demonstrated abnormalities in vestibular processing suggesting impaired central integration, thus providing unique insights into potential mechanisms contributing to symptoms of PPPD.

Summary: 

Current vestibular diagnostic techniques focus on assessment of reflexes generated by the vestibular system. While vital for identification and lateralization of peripheral end-organ involvement, approximately one third of patients have normal or non-localizing diagnostic test results, including patients with persistent postural-perceptual dizziness (PPPD). While mechanisms underlying PPPD are incompletely understood, impaired perception and integration of sensory stimuli relevant for self-motion have been proposed to be abnormal on the basis of patient report of perceptual symptoms (i.e., dizziness, vertigo) and functional neuro-imaging. As vestibular reflexes and perception use qualitatively different neural processing and arise via unique neural pathways, traditional reflexive assessments may be insensitive to changes in perception of self-motion underlying PPPD. However, vestibular perception has yet to be characterized in this patient population. Modern methods to quantify vestibular perception via perceptual thresholds have been developed and used to show that vestibular perceptual thresholds reflect changes in both peripheral and central vestibular structures, including integration of vestibular information. Thus, we hypothesized that vestibular perceptual thresholds should provide unique insights into vestibular processing in this patient population. Specifically, we hypothesized that overall vestibular perception would be impaired, reflected in overall increased thresholds, and the largest deficits would be noted on measures assessing central integration. In this study, vestibular perceptual thresholds were assessed using a one-interval direction recognition task in patients with PPPD and age- and gender-matched asymptomatic participants. The test battery assessed perception mediated by isolated canal (yaw, right-anterior left-posterior, and left-anterior right-posterior rotations) and otolith (earth-horizontal inter-aural and superior-inferior translations) function. Additionally, central integration of vestibular cues was assessed using medio-lateral tilts from upright (i.e., earth-horizontal roll-tilts), which require integration of canal and otolith cues, and translations aligned with gravity (i.e., earth-vertical translations), which require central processing to disambiguate linear acceleration from gravity. Vestibular threshold metrics were analyzed using mixed effects models to assess differences between participant groups (i.e., PPPD and healthy controls). Patients with PPPD displayed vestibular thresholds similar to healthy controls when each end-organ was stimulated in isolation, suggesting that global vestibular perception was not impaired. However, perceptual thresholds that required integration of vestibular cues, specifically roll-tilt and earth-vertical translations, were elevated, suggesting impaired processing. The pathophysiology of PPPD is incompletely characterized, and while vestibular perception has been posited to be abnormal, this is the first study to broadly and directly assess vestibular perception in this patient population. Our results suggest that vestibular perception may be abnormal in patients with PPPD, providing both insights into underlying mechanisms and potentially informing future diagnostic techniques and interventions in this patient population.