Vestibular Function in CANVAS Patients: Qualitative and Quantitative vHIT Analysis

Background/Objectives: Vestibular dysfunction is an important feature of cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS) associated with biallelic RFC1 expansions. This study aimed to characterize both quantitative and qualitative vHIT findings in genetically confirmed CANVAS patients. Methods: Fifteen patients with genetically confirmed CANVAS underwent a clinical neuro-otological assessment including horizontal video Head Impulse Test (vHIT). Quantitative analysis included vestibulo-ocular reflex (VOR) gain measurements, while qualitative analysis focused on corrective saccade characteristics, including number, peak velocity, latency interval, temporal organization, and predominant compensatory pattern. Correlations between vestibular parameters, disease duration, and clinical severity assessed using the Scale for the Assessment and Rating of Ataxia (SARA) were explored. The study specifically focused on the quantitative and qualitative characteristics. Results: All patients exhibited bilateral vestibular dysfunction, with markedly reduced VOR gains and generally low interaural asymmetry, confirming severe and largely symmetric vestibular hypofunction. Disease duration negatively correlated with VOR gain and positively correlated with the number of corrective saccades. Lower VOR gains were significantly associated with larger corrective saccades and wider latency intervals, while saccadic amplitude and latency were positively correlated. Qualitative analysis revealed a consistent pattern of predominantly overt, temporally dispersed (anisochronous) corrective saccades, with no evidence of predominant covert responses or isochronous clustering. The relationship between vestibular impairment and clinical severity was variable, suggesting partially independent progression of vestibular and cerebellar dysfunction. Conclusions: In this cohort of genetically confirmed CANVAS patients, severe, bilateral, and largely symmetric vestibular hypofunction was observed, together with a predominantly overt and temporally dispersed corrective saccade pattern. Qualitative analysis of horizontal vHIT responses may provide complementary information to conventional VOR gain measurements and may contribute to a more detailed characterization of vestibular and oculomotor findings in RFC1-related disease.