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°/s and that in the healthy-ear-down position was 19.1°/s. The mean value of MSV of the vertical component in the affected-ear-down position was 8.7°/s and that in the healthy-ear-down position was 3.0°/s. The mean value of MSV of the torsional component in the affected-ear-down position was 12.8°/s and that in the healthy-ear-down position was 6.5°/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).