The mechanics of benign paroxysmal vertigo.

Benign paroxysmal vertigo (BPV) is a disorder of the vestibular labyrinth. The clinical features can be explained by an abnormality in the posterior semicircular canal. Under the influence of gravity, a density differential between the endolymph and the cupula will cause displacement of the cupula when changes in head position occur. The presence or absence of fatiguability is a useful test as it helps define etiology, prognosis, and therapy. At the risk of adding yet another classification of nystagmus to the literature, we submit that division of BPV into two types (fatiguable and nonfatiguable) will simplify and rationalize the management of this common complaint.