Horizontal canal benign positional vertigo.

The existence of horizontal canal benign positional vertigo (BPV) was predicted from temporal bone studies in 1973, but was not clinically confirmed until later. In this series of 300 patients with BPV, 35 (12%) were identified as having the horizontal canal variant. The essential features are the onset of vertigo when the patient assumes a supine position and bidirectional horizontal nystagmus as the head is turned from side to side. In one third it appeared as a canal "conversion" in patients undergoing repositioning treatment for posterior canal BPV. The mechanism can be canalithiasis or cupulolithiasis. Repositioning treatment is a 360 degrees horizontal head and body rotation that has a high success rate if the symptomatic ear is correctly identified.