Accurate lateralization is important to improve treatment outcomes in horizontal semicircular canal (HSCC) benign paroxysmal positional vertigo (BPPV). To determine the involved side in HSCC-BPPV, the intensity of nystagmus has been compared in a head-roll test (HRT) and the direction of nystagmus was evaluated in a bow and lean test (BLT). The aim of this study is to compare the results of a BLT with those of a HRT for lateralization of HSCC-canalolithiasis and cupulopathy (heavy cupula and light cupula), and evaluate treatment outcomes in patients with HSCC-canalolithiasis. We conducted retrospective case reviews in 66 patients with HSCC-canalolithiasis and 63 patients with HSCC-cupulopathy. The affected side was identified as the direction of bowing nystagmus on BLT in 55 % (36 of 66) of patients with canalolithiasis, which was concordant with the HRT result in 67 % (24 of 36) of cases (concordant group). Lateralization was determined by comparison of nystagmus intensity during HRT in 30 patients who did not show bowing or leaning nystagmus. The remission rate after the first treatment was 71 % (17 of 24) in the concordant group and 45 % (5 of 11) in the discordant group. Both bowing and leaning nystagmus were observed in all patients with cupulopathy, and the side of the null plane was identified as the affected side. In conclusion, bowing and/or leaning nystagmus were observed in only 55 % of patients with HSCC-canalolithiasis, and the first treatment based on the result of BLT alone was effective in only 45 % of the patients in whom the BLT and HRT were discordant, which may suggest that the usefulness of BLT in lateralizing the HSCC-canalolithiasis may be limited.

Benign paroxysmal positional vertigo (BPPV) involving horizontal semicircular canal (HSCC) is characterized by direction-changing positional nystagmus (DCPN) in a supine roll test, and the occurrence of spontaneous nystagmus in HSCC BPPV has been reported recently. The aim of this study is to investigate the characteristics of pseudo-spontaneous nystagmus (PSN) in patients with HSCC canalolithiasis, and evaluate the effect of the presence of PSN on treatment outcome.Between April 2014 and January 2016, 75 and 59 patients with HSCC canalolithiasis and cupulolithiasis, respectively, were enrolled. Spontaneous and positional nystagmus were examined.PSN was observed in 31 of 75 patients (41%) with HSCC canalolithiasis, and 55 of 59 patients (93%) with HSCC cupulolithiasis. PSN persisted during the period of observation, which was at least 1 minute in all patients with PSN. In HSCC canalolithiasis, direction-reversing nystagmus was observed in 58 patients (25 bilateral and 33 unilateral). Nine of 25 patients with bilateral direction-reversing nystagmus, and 22 of 33 patients with unilateral direction-reversing nystagmus showed PSN. None of 17 patients without direction-reversing nystagmus showed PSN. The direction of PSN corresponded to that of direction-reversing nystagmus in all 22 patients with unilateral direction-reversing nystagmus. The proportion of patients who recovered after 1 session of repositioning maneuver was not significantly different between patients with and without PSN (P = .867).PSN was observed more commonly in HSCC cupulolithiasis than canalolithiasis. The pathophysiologic mechanism underlying PSN can be explained by natural inclination of HSCC and medial to lateral orientation of the HSCC cupular axis in cupulolithiasis, and by spontaneous reversal of initial positional nystagmus (direction-reversing nystagmus) generated by short-term adaptation of vestibulo-ocular reflex in canalolithiasis. The presence of PSN in HSCC canalolithiasis may not affect the treatment outcome.

Conclusion The patients with serous labyrinthitis caused by acute otitis media (AOM) exhibited various patterns of nystagmus in which direction-fixed irritative-type nystagmus was the most common pattern. Differential effects on inner ear function by toxic or inflammatory mediators may be responsible for the various manifestation of nystagmus. Objective This study aimed to investigate nystagmus patterns in patients with serous labyrinthitis, and discuss possible mechanisms. Methods From October 2011 to March 2014, 13 consecutive patients with serous labyrinthitis were included. Eye movements of the patients were serially examined using video-nystagmography, and patterns of nystagmus were investigated. Results The most commonly observed pattern was direction-fixed nystagmus (nine of 13 patients). Of these, eight showed irritative-type, and one showed paretic-type. Direction of nystagmus, although the intensity gradually decreased, was not changed during the course of treatment. One patient showed direction-changing spontaneous nystagmus, which changed into paretic-type direction-fixed nystagmus 1 day after myringotomy. Three patients exhibited persistent direction-changing positional nystagmus in a supine head-roll test. Of them, two showed apogeotropic and one showed geotropic type. In all 13 patients, vertigo and hearing loss were improved after the treatment.