Preserved otolith function in patients with cerebellar atrophy and bilateral vestibulopathy

Cerebellar degeneration affects vestibular function. For instance, with lesions of the cerebellar flocculus, the ability to adaptively modify the VOR gain is markedly reduced, and cerebellar patients may even demonstrate severe vestibular deficits. We report five patients (m=3, f=2) with cerebellar disease, in whom search-coil head impulse testing revealed reduced gains of the angular VOR, while sacculus-mediated myogenic potentials were normal. Preserved static ocular counterroll in roll-tilt positions and prominent gravity-dependent modulation of downbeat nystagmus (DBN) along the pitch plane demonstrated the integrity of otolith (OL) function in these patients as well. Probably, at least in some cerebellar patients with marked floccular atrophy, the dissociation between impaired semicircular canal (SCC) function and preserved OL function may be explained by a predilection of the atrophic process for the flocculus and brainstem neurons involved in angular VOR gain control, while structures mediating OL function remain widely spared by the cerebellar degeneration. The exact pathomechanism leading to the vestibular impairment remains unclear: both a primary multi-system-type atrophy involving cerebellar and brainstem vestibular structures as well as a mechanism of secondary retrograde degeneration of floccular brainstem target neurons mediating SCC function seem plausible.