Cerebellar Ataxia, Neuropathy, & Vestibular Areflexia Syndrome (CANVAS): Impaired Visually-Enhanced VOR and Abnormal Head Impulse Testing

A 67 year old woman presented with 1 year of progressive numbness, gait instability, and oscillopsia when walking or with head movements. Examination showed excessive square-wave jerks, bilateral horizontal gaze-evoked nystagmus, impairment of the visually-enhanced vestibular ocular reflex (vVOR - see with slow head turning to the right and left, which is a combination of pursuit and the VOR), and impairment of the vestibular ocular reflex (VOR) during head impulse testing, in the planes of all 6 canals (horizontal, posterior and anterior). Sensory testing also showed impaired vibration in the distal extremities. A clinical diagnosis of cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS) was made. An impaired or saccadic vVOR suggests that there is failure of both the pursuit and (bilateral) vestibular systems, and CANVAS should be considered, especially when neuropathy is present. Other conditions that should be considered if the vVOR is impaired include Wernicke's encephalopathy if the symptom onset is acute, and if the course is more chronic, the neurodegenerative processes including multiple system atrophy as well as some of the spinocerebellar ataxias (types 1, 3, 4, 6 among several others) could be responsible