Otolith function in Usher type II syndrome.

Background: Usher's syndrome type II (USH2) is a rare genetic disorder encompassing hearing loss, vision impairment, and apparent intact vestibular function. Recent research suggests a potential involvement of the otolith vestibular receptors in USH2.
Aims/objectives: Evaluate otolith dynamic function in USH2.
Material and Methods: Twenty-two USH2 (median age 53.9 ± 2.99) and age-matched controls underwent a complete battery vestibular testing including air conducted cervical and ocular vestibular evoked myogenic potentials (c-VEMPs and o-VEMPs). Vestibular function tests were correlated with Activities Balance Scale (ABC) and Dizziness Handicap Inventory (DHI) scores.
Results: Fourteen USH2 reported previous vertigo (vs none control). Among 88 ears, c-VEMPs were absent in 15 USH2 cases and 4 controls ( p  = 0.034), while o-VEMPs were absent in 22 USH2 cases and 12 controls ( p  = 0.129). There were significant differences between USH2 vs controls in right ear o-VEMP N1 latencies (median 11.60/10.40, p  < 0.010), N1-P1 amplitudes (median 5.15/10.10, p  < 0.003) and in o-VEMP N1-P1 asymmetry ratio (median 24.78/40.50, p  < 0.014). USH2 showed a strong correlation between o-VEMP amplitude and DHI score ( p  = 0.003, ρ = 0.769). No association was found between vertigo and VEMPs subgroups.
Conclusions and Significance: Our findings suggest the presence of otolith dysfunction in USH2, which is independent from subjectively reported dizziness. Incorporating vestibular testing into USH2 evaluation and monitoring could enhance characterization of this multisensory disease.