Pearls & Oy-sters: Vibration-Induced Downbeat Nystagmus: A New Cerebellar Sign Observed in Paraneoplastic Syndrome

Vibratory stimulation of the sternocleidomastoid muscles or the skull may enhance vestibular asymmetry and evoke nystagmus. We report prominent downbeating vibration-induced nystagmus (VIN) in a patient with paraneoplastic cerebellar degeneration due to cervical cancer with positive serum anti-Ri antibody. A 47-year-old woman developed spontaneous upbeat nystagmus present with and without visual fixation. Nystagmus decreased during lateral and upward gaze. Downbeat nystagmus emerged during convergence and after horizontal head shaking for approximately 15 seconds and during vibratory stimulation of the mastoids and forehead. Additional findings included positional downbeat nystagmus, impaired smooth pursuit, hypermetric horizontal saccades, and truncal ataxia. During video-head impulse tests, the gains of the vestibulo-ocular reflex (VOR) were normal for both horizontal semicircular canals but increased for both anterior canals and decreased for both posterior canals. Horizontal head impulses produced cross-coupled downward corrective saccades. Given the asymmetric vertical VOR, downbeat VIN observed in our patient may be ascribed to enhanced upward bias of the VOR due to vestibulocerebellar dysfunction during the vibratory stimuli. Vibration-induced downbeat nystagmus should be added to the list of central vestibular signs and is likely due to cerebellar dysfunction.