Positional Downbeat Nystagmus

Abstract

Positional downbeat nystagmus is one of the common forms of central positional nystagmus. It has been reported in various structural, metabolic, or degenerative disorders affecting the inferior cerebellum. According to the temporal characteristics, it can be divided into the paroxysmal form that is usually evident after lying down or straight head-hanging (backward pitch rotation) and the persistent form that is mostly observed in the static prone head position. The paroxysmal form of central positional downbeat nystagmus may be ascribed to a pathologically enhanced post-rotational cue. In contrast, the persistent form has been explained by hyperactive otolith-ocular reflex or by a bias in estimated gravity direction in the head coordinate frame. Positional downbeat nystagmus may be observed in benign paroxysmal positional vertigo. Characteristics of the nystagmus and associated neuro-otological findings may allow differentiating central from peripheral positional downbeat nystagmus.