Utility of the bow and lean test in predicting subtype of benign paroxysmal positional vertigo

Objectives/Hypothesis: To investigate the role of the bow and lean test (BLT) in the diagnosis of benign paroxysmal positional vertigo (BPPV). Study Design: Retrospective case-control study. Methods: Between March 2015 and June 2017, we enrolled 113 patients with posterior semicircular canal (PSCC) BPPV, 74 patients with lateral semicircular canal (LSCC) canalolithiasis, 53 patients with LSCC cupulolithiasis, and 32 patients with light cupula. We retrospectively assessed bowing nystagmus (BN) and leaning nystagmus (LN). Results: In PSCC BPPV, 75% of the patients showed at least one of BN and LN, and direction of nystagmus provoked by a Dix-Hallpike test on the affected side was consistent with that of LN and opposite to that of BN. In LSCC canalolithiasis, 65% (48 of 74) of the patients showed both BN and LN, which were in the same direction in 38 patients (of 48) and in the opposite direction in 10 patients (of 48). The affected side can be determined according to the results of THE BLT in 74% (55 of 74) of LSCC canalolithiasis patients, and among them, the side determined according to the results of head-roll test was discordant with that according to the BLT in 20 of 55 patients (36%). In LSCC cupulopathy (n = 85), both BN and LN were persistent and observed in all cases, but we could not distinguish LSCC cupulolithiasis from light cupula according to nystagmus direction in the BLT. Conclusions: Although a BLT yields better lateralization in LSCC canalolithiasis, it may be more useful in predicting the diagnosis and lateralization of PSCC BPPV than LSCC canalolithiasis.