Clinical Implications of Horizontal Beating Nystagmus Induced by Dix-Hallpike Test in the Diagnosis of Horizontal Canal Benign Paroxysmal Positional Vertigo

OBJECTIVES The purpose of this study was to identify the diverse patterns of nystagmus during the Dix-Hallpike test (DHT) and analyze their clinical significance in horizontal canal benign paroxysmal positional vertigo (HC-BPPV). STUDY DESIGN Retrospective medical records review. PATIENTS Two hundred ninety-five patients diagnosed with HC-BPPV. METHODS Various nystagmus patterns identified during the DHT in patients with HC-BPPV were analyzed. The correlation between the affected side of HC-BPPV and the direction of the horizontal beating nystagmus (HBN) during the DHT was also analyzed. RESULTS The nystagmus pattern during the DHT in 128 patients with geotropic HC-BPPV demonstrated, direction-changing positional nystagmus on both sides in 48 (37.5%) patients, HBN toward one side in 25 (19.6%) patients, and no nystagmus in 55 (42.9%) patients. In 144 patients with apogeotropic HC-BPPV, 54 (37.5%) patients presented with direction-changing positional nystagmus on both sides, 27 (18.8%) patients presented with HBN toward one side, and 63 (43.7%) patients did not show nystagmus during the DHT. The direction of HBN provoked by the DHT was significantly correlated with the affected side in each subtype of HC-BPPV (geotropic type, p = 0.049; apogeotropic type, p = 0.040; respectively). CONCLUSION More than half of the patients with HC-BPPV (56.6%) showed HBN during the DHT. When HBN was present during the DHT, it may provide a clue for determining the subtype and affected side in diagnosis of HC-BPPV before performing the supine roll test.