Nystagmus and postural instability after headshake in patients with vestibular dysfunction

Nystagmus after rapid head‐shaking (post‐headshake nystagmus) is often seen in patients with vestibulopathy. Post‐headshake nystagmus is transient and is frequently associated with symptoms of dizziness, dysequilibrium, or vertigo. The phenomenon presumably reflects headshake‐induced asymmetry in vestibulo‐ocular reflex pathways, which persists after head‐shaking stops. We postulated that the same vestibular imbalance that underlies post‐headshake nystagmus might produce an equivalent in postural instability. To test this hypothesis, we investigated the effect of headshake on postural control and eye movements in patients who exhibited post‐headshake nystagmus, vestibulopathy, or both. Postural instability was quantified with a dynamic platform device, whereas eye movements were recorded with electrooculography. Ten normal controls and 21 patients with a history of post‐headshake nystagmus or unilateral vestibulopathy were evaluated. Subjects were tested for 20 seconds before and immediately after passive horizontal headshake (±30‐degree amplitude) at 2 Hz for 20 seconds. Postural stability was assessed while subjects stood with eyes closed, and the floor was modulated proportionally with sway. The difference in normalized peak‐to‐peak sway (equilibrium score) before and after headshake was assessed in all subjects and compared between groups. Post‐headshake nystagmus was documented by electro‐oculography recorded during posturography. Results for normal controls and vestibulopathic subjects without post‐headshake nystagmus showed only a small transient decline in postural stability after headshake. Those with post‐headshake nystagmus (regardless of caloric asymmetry) showed a robust decline in postural stability. The most dramatic decline, together with an increased number of “falls” (step‐out responses), occurred in those patients with both a vestibulopathy (caloric response asymmetry) and post‐headshake nystagmus. These findings illustrate that the vestibular imbalance underlying post‐headshake nystagmus shares a counterpart in the form of headshake‐induced postural instability.