Nystagmus while recumbent in horizontal canal benign paroxysmal positional vertigo

Background: The identification of the affected ear is crucial for the successful treatment of benign paroxysmal positional vertigo involving the horizontal canal (HC-BPPV) by using particle-repositioning maneuvers. Objective: To determine the lateralizing value of lying-down nystagmus in HC-BPPV. Methods: The authors prospectively investigated lying-down nystagmus in 152 consecutive patients with confirmed HC-BPPV ( 99 geotropic and 53 apogeotropic types). Lying-down nystagmus was induced by placing patients in a supine position. For the geotropic type of HC-BPPV, the affected ear was identified by assuming that nystagmus is more intense when the head is rotated to the affected side while supine. The reverse assumption was adopted for the apogeotropic type. Results: Lying-down nystagmus was observed in 58 patients (38.2%), 36 (36.4%) of the geotropic and 22 (41.5%) of the apogeotropic type. The direction of lying-down nystagmus was mostly away from the affected ear in the geotropic type, but toward the affected ear in the apogeotropic type. Of the 16 geotropic patients in whom the affected ear was not identified initially, 7 with lying-down nystagmus showed resolution of vertigo after particle-repositioning maneuvers when the involved ear was identified by observing lying-down nystagmus. Conclusion: Lying-down nystagmus is a valuable sign for determining which ear is affected in benign paroxysmal positional vertigo involving the horizontal canal, especially when patients show symmetric nystagmus on turning the head to either side.