Reverse Nystagmus During Canalith Repositioning: A Misunderstood Predictor of Failed Epley Maneuver: A Retrospective Study Based on 60 Patients with Posterior Semicircular Canal BPPV.

Objective: To analyze the types, directions, and intensities of nystagmus occurring during each step (positions 2, 3, and 4) of the Epley maneuver in patients with posterior semicircular canal benign paroxysmal positional vertigo (BPPV), and to explore their relationship with a positive Dix-Hallpike test at 24-48 hours post-maneuver, indicating incomplete canalith clearance. Methods: Clinical data from 60 patients with unilateral posterior semicircular canal canalithiasis were retrospectively analyzed. All patients underwent a standard Epley maneuver under video nystagmography (VNG) monitoring. The direction and slow phase velocity (SPV) of nystagmus were recorded at each repositioning step. The need for a second repositioning was determined by repeat Dix-Hallpike test 24-48 hours after the maneuver. Univariate and multivariate logistic regression analyses were performed to identify associations between nystagmus characteristics at each step and the need for a second procedure. Sensitivity, specificity, and predictive values were calculated. Results: Among 60 patients, 19 (31.7%) required a second repositioning. Univariate analysis showed that reverse nystagmus at position 3, reverse nystagmus at position 4, reverse nystagmus at either position 3 or 4, SPV of reverse nystagmus at position 4 ≥10°/s, diagnostic vertical SPV ≥20°/s, and latency ≤2 s were significantly associated with the need for a second procedure (all P<0.01). Multivariate logistic regression identified reverse nystagmus at position 4 as the strongest independent predictor (OR=32.1, 95%CI 6.2-166.7). Reverse nystagmus at position 4 predicted the need for a second procedure with a sensitivity of 84.2%, specificity of 97.6%, positive predictive value of 94.1%, and negative predictive value of 93.0%. Although reverse nystagmus at position 3 was also associated with the need for a second procedure (OR=18.5), its sensitivity was low (47.4%). Orthotropic nystagmus at position 2 showed no correlation with outcome (P>0.05). All four patients who exhibited down-beating nystagmus did not require a second procedure. Conclusion: During the Epley maneuver, reverse nystagmus occurring at position 4 is the strongest predictor of the need for a second repositioning, with a positive predictive value exceeding 94%. Down-beating nystagmus indicates a favorable outcome and was associated with a lower probability of requiring a second repositioning. Real-time nystagmus feedback during the procedure allows early identification of high-risk patients and enables optimized, individualized follow-up strategies.