Evaluation of the Diagnostic Value of Video-oculography in CANVAS Neuronopathies

Cerebellar Ataxia

Cerebellar ataxia syndrome with neuropathy and vestibular areflexia (CANVAS) is a genetic pathology of recent discovery (bi-allelic expansion in intron 1 of the RFC1 gene with AAGG repetition). The clinical picture is protean, associating a neuronopathy, a bilateral vestibulopathy evidenced by an alteration of the oculovestibular reflex (VOR), an atrophy of the cerebellum and a chronic cough. In the initial stage of the disease the clinical picture is heterogeneous and often incomplete. Ataxia at the beginning of the disease may be the consequence of peripheral nervous system involvement (neuronopathy) and the cerebellar syndrome may manifest itself clinically late. Eye movement involvement in central nervous system pathologies is common (4). Oculomotor abnormalities are often subclinical and sometimes exclusively identifiable by an instrumental study, video-oculography (VOG) (5). VOG is a non-invasive examination of eye movements, which is increasingly used in the differential diagnosis of neurodegenerative syndromes (6). This examination allows, among other things, to identify oculomotor anomalies, even discrete and asymptomatic, by studying the combined movements of the eyes and the oculocephalic movements. The study of oculomotricity by VOG can therefore potentially contribute to the early differential diagnosis of ataxiating neuropathies, including CANVAS, by revealing infra-clinical oculomotor abnormalities correlated with a cerebellar expectation (knowing the role of the dorsal vermis in the precision of saccades and pursuits).

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