title: Nystagmus and postural instability after headshake in patients with vestibular dysfunction.
abstract: 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.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Neurology, University of Rochester School of Medicine and Dentistry, NY.
authors.forename: M S
authors.initials: MS
authors.lastname: Panosian
authors.forename: G D
authors.initials: GD
authors.lastname: Paige
mesh_terms: D000328:Adult; D000368:Aged; D002150:Caloric Tests; D004244:Dizziness / Q000503:physiopathology; D004584:Electronystagmography; D004585:Electrooculography; D005133:Eye Movements / Q000502:physiology; D006257:Head / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D009068:Movement; D009759:Nystagmus, Pathologic / Q000209:etiology* / Q000503:physiopathology; D004856:Postural Balance / Q000502:physiology; D011187:Posture / Q000502:physiology*; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology; D014717:Vertigo / Q000503:physiopathology; D015837:Vestibular Diseases / Q000150:complications* / Q000503:physiopathology