The clinical significance of head-shaking nystagmus in the dizzy patient.

The clinical significance of horizontal head-shaking nystagmus (HSN) was evaluated in 85 patients who complained of dizziness and vertigo. This was done by comparison of the horizontal head-shaking test with routine rotatory and caloric vestibular testing. We found that HSN evoked by horizontal head-shaking is a highly sensitive way to detect unilateral vestibular hypofunction. Except in patients with additional central vestibular imbalance or in patients with Meniere's disease, the direction of horizontal HSN is highly significant in indicating the side of the lesion, with the fast phase beating toward the intact side. However, horizontal HSN is not specific in distinguishing peripheral hypofunction from more central vestibular imbalances. Peripheral vestibular hypofunction as well as a central asymmetry of the vestibular velocity storage mechanism can each separately or in combination produce horizontal HSN. Thus, while the head-shaking manoeuvre is an excellent bedside-test to detect unilateral vestibular hypofunction, further rotatory and caloric testing is still necessary to clarify the patient's condition.