Vestibular falls.

Vestibular dysfunction is a significant differential diagnosis in patients who have unexpected falls without: loss of consciousness, paresis, sensory loss, or cerebellar deficit. Either peripheral or central vestibular disorders cause postural instability with preferred directions of falling, some of which can be attributed to either the particular plane of the affected semicircular canal or a central pathway mediating the 3-dimensional vestibulo-ocular reflex in yaw, pitch, and roll. Ipsiversive falls occur in vestibular neuritis or in Wallenberg's syndrome--where they are known as lateropulsion. Contraversive falls are typical for the otolith Tullio phenomenon, vestibular epilepsy, and thalamic astasia. Predominant fore-aft instability is observed in bilateral vestibulopathy, benign paroxysmal positioning vertigo, as well as in downbeat or upbeat nystagmus syndrome. Falls can be diagonally forward (or backward) and toward or away from the side of the lesion, depending on the site of the lesion (the ocular tilt reaction is ipsiversive in medullary lesions, but contraversive in mesencephalic lesions) and on whether vestibular structures are excited or inhibited.