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

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 repo-sitioning 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.