Hyperventilation-induced nystagmus in patients with vestibular neuritis in the acute and follow-up stages.

OBJECTIVE

Our purposes were to characterize hyperventilation-induced nystagmus (HVIN) in patients with unilateral vestibular neuritis (VN) through follow-up examinations and to determine the effects of hyperventilation on vestibular imbalance in patients with VN.

MATERIALS AND METHODS

The horizontal eye movements in 35 patients with acute VN were recorded. The eye movements were analyzed and the maximum value of slow-phase eye velocity (SPV) was obtained during and after hyperventilation. Nineteen of 35 patients underwent follow-up examinations around 7 weeks later. When spontaneous nystagmus was present, the SPV of spontaneous nystagmus was subtracted from that of HVIN. A maximum SPV of HVIN of ≥4°/s was considered abnormal. The direction and SPV of HVIN were analyzed.

RESULTS

The incidence of HVIN in patients with VN was significantly higher in the acute stage (18 of 35; 51%) than the follow-up stage (4 of 19; 21%). The direction of HVIN present in the follow-up stage was entirely towards the contralesional side (contralesional HVIN). However, the direction of HVIN in the acute stage was mixed, towards the contralesional side (10 of 35; 28%) and towards the ipsilesional side (8 of 35; 23%). The SPVs (49 ± 56°/s) of ipsilesional HVIN were significantly greater than the contralesional HVIN in the acute stage (8 ± 3°/s). Robust nystagmus (SPV ≥ 25°/s) was entirely ipsilesional HVIN, which was observed only in the acute stage.

CONCLUSIONS

Our findings indicate that hyperventilation can result in aggravation of vestibular imbalance in the acute and follow-up stages in different ways. Hyperventilation resulted in contralesional HVIN in both the acute and follow-up stages, each in approximately a fourth of the patients, which suggests a disruption of central static compensatory mechanisms. However, ipsilesional HVIN was elicited only in the acute stage (in approximately a fourth of the patients). About half of the patients with ipsilesional HVIN showed robust responses, which is a characteristic finding, suggesting a transient intense increase in vestibular activity on the lesional side.