Kinetic classification of posterior semicircular canal canalithiasis based on quantitative nystagmus parameters and its predictive value for the need of a second Epley maneuver: a retrospective quantitative analysis of 60 patients.

OBJECTIVE: To classify the kinetic state of otoconia in canalithiasis according to the slow phase velocity (SPV) of nystagmus during the Dix‑Hallpike test in patients with posterior semicircular canal benign paroxysmal positional vertigo (PSC‑BPPV), and to evaluate the association between different subtypes and the need for a second Epley maneuver, thereby establishing a prognostic model based on kinetic classification. METHODS: Clinical data of 60 patients with unilateral PSC canalithiasis were retrospectively analyzed. Receiver operating characteristic (ROC) curves were used to determine the optimal threshold of diagnostic vertical SPV for predicting the need for a second repositioning. Patients were subsequently divided into a high‑SPV aggregated type and a low‑SPV dispersed type based on better prognostic discrimination in clinical grouping (threshold = 20%). The direction and SPV of nystagmus during each step of the Epley maneuver were recorded. The primary outcome was a positive Dix‑Hallpike test 24-48 hours after the initial maneuver, indicating the need for a second repositioning. The rates of second repositioning and the characteristics of inhibitory nystagmus during the maneuver were compared between the two types. Logistic regression was used to analyze the independent predictive value of the classification. RESULTS AND DISCUSSION: ROC curve analysis showed that the area under the curve (AUC) of diagnostic vertical SPV for predicting a second repositioning was 0.85 (95% CI 0.76-0.94, p < 0.001). 21 patients (35.0%) were classified as high‑SPV aggregated type (vertical SPV ≥20°/s) and 39 patients (65.0%) as low‑SPV dispersed type (vertical SPV <20°/s). The rate of second repositioning was 14.3% (3/21) in the high‑SPV aggregated type and 41.0% (16/39) in the low‑SPV dispersed type (χ 2 =, p =0.041). Among patients with inhibitory nystagmus at step 4, the low‑SPV dispersed type had a high second‑session rate of 84.6% (11/13). Multivariate logistic regression showed that both the low‑SPV dispersed type (OR=4.7, 95% CI 1.2-19.3, p = 0.031) and inhibitory nystagmus at step 4 (OR=14.5, 95% CI 3.1-68.2, p < 0.001) were independent predictors of the need for a second repositioning. The events-per-variable ratio was approximately 9.5:1, which is acceptable but relatively modest; thus, the results warrant cautious interpretation. These findings are exploratory and require validation in independent external cohorts.