Horizontal canal BPV.

Benign paroxysmal vertigo (BPV) is generally attributed to a differential density condition in the posterior semicircular canal. Although the posterior canal is implicated because of its dependent position, the possibility exists that either the horizontal or superior canal could become involved. This paper reports on seven patients with a clinical picture consistent with horizontal canal BPV. The characteristic features are brief vertigo and horizontal nystagmus precipitated by head movement into or out of one of the lateral positions. Position change toward the left lateral position induces left beating nystagmus and vice versa for position change toward the right. The direction of the nystagmus indicates a utriculopetal "endolymph flow" when the affected horizontal canal is undermost. This could be explained by particle movement or a "viscous plug" in the posterior aspect of the canal.