Downbeat Nystagmus in Cerebellitis: The Cerebellar Inhibition to the Vestibulo-Ocular Reflex.

Abstract

Downbeat nystagmus occurs as a result of an impaired vestibulo-ocular reflex1. From animal experiments, the Purkinje cells of the flocculonodular and parafloccular lobes of the cerebellum (also known as the “vestibular cerebellum”) are known to negatively regulate the upward rotation of the eyes via feed-forward inhibitory neural circuitry to the vertical vestibulo-ocular reflex [Supplemental figure 1,links.lww.com/CPJ/A199) 2. Although various eye movement abnormalities have been described in congenital and acquired cerebellar disorders, there have been few reports of pure downbeat nystagmus in cerebellitis.Here we report a quite impressive pure downbeat nystagmus in an adolescent female with acute cerebellitis. The electro-oculography of the patient provided compelling evidence that the downbeat nystagmus is indeed the result of feed-forward inhibition to the vestibulo-ocular reflex. Our case may add new insights into the current literature on cerebellar control of eye movement.