Positional nystagmus of horizontal canalolithiasis

Conclusion: Vertical and torsional components occur from the horizontal semicircular canal, and the response to ampullopetal flow is greater than that to ampullofugal flow in every component. Objectives: To clarify whether positional nystagmus of horizontal canalolithiasis contains vertical and torsional components, and to quantify the asymmetry of nystagmus. Methods: Twenty patients with transient direction-changing geotropic positional nystagmus were examined, and we performed three-dimensional video-oculography and measured the maximum slow-phase velocity (MSV) of three components. Results: Positional nystagmus was not purely horizontal. Fifteen (75%) patients revealed a vertical component and 19 (95%) patients had a torsional component. The mean value of MSV of the horizontal component in the affected-ear-down position was 51.5 degrees/s and that in the healthy-ear-down position was 19.1 degrees/s. The mean value of MSV of the vertical component in the affected-ear-down position was 8.7 degrees/s and that in the healthy-ear-down position was 3.0 degrees/s. The mean value of MSV of the torsional component in the affected-ear-down position was 12.8 degrees/s and that in the healthy-ear-down position was 6.5 degrees/s. For every component, MSV in the affected-ear-down position was significantly greater than that in the healthy-ear-down position (p < 0.01).