Vestibulo-Ocular Reflex Impairment without Saccular Dysfunction in Machado-Joseph Disease

Background: Although ocular motor abnormalities are frequent in all forms of Spinocerebellar ataxias (SCAs), vestibulo-ocular reflex (VOR) deficit seems to be a characteristic of SCA-3 (Machado-Joseph disease -MJD). However, all previous studies were focused on lateral semicircular canals function without information regarding the anterior and posterior canal responses and the otolithic function. The aim of this study was to evaluate the three semicircular canals VOR responses and otolithic function in Jew Yemenite patients with SCA-3 in a search for a better neurophysiologic biomarker of the disease.

Methods: Sixteen MJD patients underwent a detailed clinical and laboratory neuro-otological evaluation including horizontal and vertical VOR recordings with the video head impulse test (vHIT) system. Eight of them underwent also cervical vestibular evoked myogenic potentials (cVEMPs) by bilateral tone burst stimulation measuring otolithic saccular function.

Results: All MJD patients had significant angular VOR gain decrease (about 50% of normal values) in both horizontal and vertical planes. cVEMPs responses (latency and amplitude of P13 and N23) were normal in all eight examined patients. Ataxia severity evaluated by the Scale for the Assessment and Rating of Ataxia (SARA) was mildly correlated with the degree of VOR impairment.

Conclusion: Angular VOR impairment in horizontal and vertical planes seems to be a distinctive feature of MJD and could be explained by selective rostral vestibular nuclei degeneration. We suggest that quantitative VOR measures could probably be a neurophysiologic biomarker for detecting the appearance and progression of neuro-degeneration in MJD.