Abnormal Visually-Enhanced VOR in Cerebellar Ataxia, Neuropathy, Vestibular Areflexia Syndrome (CANVAS)

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). Normally, when a high velocity but low amplitude movement of the head is applied (i.e., high enough velocity that the smooth pursuit system fails while the VOR system is isolated), the patient's eyes stay on their intended target, which is typically the examiner's nose (https://collections.lib.utah.edu/details?id=187678). This is a normal or negative head impulse test and suggests a normal VOR toward the side of the impulse. In contrast, if the eyes initially move with the head in the direction of the impulse and then need to make a catch-up saccade, this is an abnormal or positive impulse test (https://collections.lib.utah.edu/details?id=187723) and suggests an abnormal VOR toward the side of the impulse. In this particular patient's case, 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.