Clinical testing of otolith function: Perceptual thresholds and myogenic potentials

Cervical and ocular vestibular-evoked myogenic potential (cVEMP/oVEMP) tests are widely used clinical tests of otolith function. However, VEMP testing may not be the ideal measure of otolith function given the significant inter-individual variability in responses and given that the stimuli used to elicit VEMPs are not physiological. We therefore evaluated linear motion perceptual threshold testing compared with cVEMP and oVEMP testing as measures of saccular and utricular function, respectively. A multi-axis motion platform was used to measure horizontal (along the inter-aural and naso-occipital axes) and vertical motion perceptual thresholds. These findings were compared with the vibration-evoked oVEMP as a measure of utricular function and sound-evoked cVEMP as a measure of saccular function. We also considered how perceptual threshold and cVEMP/oVEMP testing are each associated with Dizziness Handicap Inventory (DHI) scores. We enrolled 33 patients with bilateral vestibulopathy of different severities and 42 controls to have sufficient variability in otolith function. Subjects with abnormal oVEMP amplitudes had significantly higher (poorer) perceptual thresholds in the inter-aural and naso-occipital axes in age-adjusted analyses; no significant associations were observed for vertical perceptual thresholds and cVEMP amplitudes. Both oVEMP amplitudes and naso-occipital axis perceptual thresholds were significantly associated with DHI scores. These data suggest that horizontal perceptual thresholds and oVEMPs may estimate the same underlying physiological construct: utricular function.