Relation between the Direction of Nystagmus in the Supine Position and the Affected Side in Patients with Horizontal Semicircular Canal Benign Paroxysmal Positional Vertigo

The relation between the nystagmus in the supine position and the affected side in patients with horizontal semicircular canal benign paroxysmal positional vertigo (HC-BPPV) is studied because nystagmus is frequently observed in the supine position before the patient assumes the supine right-ear-down and left-ear-down positions. Thirty patients with HC-BPPV were examined using electronystagmography (ENG) in the supine, supine right-ear-down and supine left-ear-down positions, and the relation between the direction of nystagmus in the supine position and the affected side was studied. The direction of nystagmus in the supine position was consistent with the affected side in 11 of 18 (61%) patients with cupulolithiasis and in 7 of 12 (58%) patients with canalithiasis. ENG findings in HC-BPPV patients with cupulolithiasis suggested that the cupula is oriented laterally in the HC. Other ENG findings in HC-BPPV patients with canalithiasis suggested that otoconia are located in the medial position of the HC. These findings are helpful to infer the affected side in the patient with HC-BPPV by observation of the nystagmus in the supine position before placing the patient in the supine right/left-ear-positions.