Neurophysiological evidence for generalized sensory neuronopathy in cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome.

INTRODUCTION Cerebellar ataxia with neuropathy and bilateral vestibular areflexia syndrome (CANVAS) is a recently described multisystem ataxia defined by the presence of cerebellar ataxia, bilateral vestibulopathy, and a somatosensory deficit. The characteristic clinical sign is an abnormal visually enhanced vestibuloocular reflex. The somatosensory deficit contributes to a significant level of disability in CANVAS. METHODS This study was a neurophysiological investigation of 14 patients with CANVAS. RESULTS Findings revealed uniformly absent sensory nerve action potentials in all limbs, abnormal blink reflexes in 13 of 14 patients, and abnormal masseter reflexes in 6 of 11 patients. Tibial H-reflexes were absent in 11 of 14 patients. Somatosensory evoked potentials were abnormal in 10 of the 11 patients tested, and brainstem auditory evoked responses were abnormal in 3 of 8. Cutaneous silent period responses were abnormal in 7 of 14 patients. CONCLUSIONS We suggest that a sensory neuronopathy should be sought in cerebellar and/or vestibular ataxias, particularly where the degree of ataxia is out of proportion to the clinically identified cerebellar and/or vestibular dysfunction.