Cerebellar ataxia with bilateral vestibulopathy: description of a syndrome and its characteristic clinical sign.

We report four patients with the syndrome of cerebellar ataxia with bilateral vestibulopathy (CABV) and, using search coil oculography, we validate its characteristic clinical sign, namely impairment of the visually enhanced vestibulo-ocular reflex (VVOR) or doll's head reflex. In our four patients, CABV began in the sixth decade of life; they are still ambulant and self-caring 8-20 years after onset. The cause of CABV in our four patients is unknown. None has a family history of cerebellar or vestibular disease; spinocerebellar ataxia (SCA) 1, 2, 3, 6, 7 and Friedreich's ataxia were excluded by genetic testing. Three of the four have a sensory peripheral neuropathy but none has extrapyramidal or significant autonomic problems, and none has gluten sensitivity. We measured eye rotations in response to head-on-trunk head rotations and in response to head-and-trunk (en bloc) rotations. Horizontal smooth pursuit (SP), vestibulo-ocular reflex (VOR) and VVOR gains were measured in response to head rotations at 0.1, 0.3, 0.6 and 1.0 Hz. The optokinetic reflex (OKR) was tested by measuring optokinetic nystagmus slow phase velocity during constant 50 degrees /s rotation of the subject in light. The results showed that CABV patients had impairment of all three compensatory eye movement reflexes, the VOR, the OKR and SP. During VVOR testing, as the frequency of head rotation increased from 0.1 to 1.0 Hz, eye velocity failed to match head velocity, gaze velocity increased, and gaze position errors developed, which were corrected with bursts of saccades, the basis of the clinical sign of an impaired VVOR.