Quantitative Analysis of the Nystagmus of Posterior Canal Benign Paroxysmal Positional Vertigo and Its Association With Prognosis

OBJECTIVES: Positional nystagmus triggered by a change of head position is essential for the diagnosis and treatment of benign paroxysmal positional vertigo (BPPV). However, the quantitative data on its characteristics and prognostic value remain unclear. The objective of this study is to quantify the direction, latency, and duration of positional nystagmus in posterior canal BPPV and explore their association with treatment outcomes. DESIGN: Patients diagnosed with posterior canal BPPV were enrolled prospectively. Participants underwent positional tests and canalith repositioning procedures on a multiaxial repositioning chair with infrared video-oculography. Positional nystagmus was recorded throughout diagnosis and treatment. Modified Epley maneuver with repositioning chair was the primary treatment. For patients unresponsive to Epley maneuvers, 360° rotation was the salvage treatment. Outcomes include resolution of positional nystagmus and subjective severity of symptoms assessed by a visual analogue scale. RESULTS: A total of 285 participants were included in the final analysis. The median latency of nystagmus was 0.47 (interquartile range [IQR]: 0 to 1.3) seconds in head-hanging position of Dix-Hallpike test and 0 (IQR: 0 to 0.7) seconds in the sitting-up position, with median durations of 12.7 (IQR: 9.7 to 16.7) and 13.6 (IQR: 9.1 to 18.8) seconds, respectively. No latency was observed in 98 (34.4%) participants, but this did not affect the rate of treatment success ( p = 0.15). The severity of symptoms was positively correlated with nystagmus duration ( p = 0.003). Torsional, up-beating nystagmus in the third position of the modified Epley maneuver was a positive predictor of a successful treatment (73.0% versus 44.8%; p < 0.001), whereas torsional, down-beating nystagmus in the fourth position was not associated with treatment efficacy (68.3% versus 62.1%; p = 0.27). For refractory cases, 24 (60.0%) of 40 patients who received 360° rotation had complete resolution in 7 to 14 days. Unexpectedly, initial treatment success on day 0 was not associated with the rate of resolution or residual dizziness at 7 to 14 days. CONCLUSIONS: The latency and duration of the positional nystagmus elicited by Dix-Hallpike test had limited prognostic value in BPPV, whereas in the modified Epley maneuver, nystagmus in the third position was associated with treatment success. For refractory cases, chair-based 360° rotation is a promising alternative. Patients with residual nystagmus after treatment had comparable outcomes to those without at 7 to 14 days.