Work

Assessment: Vestibular testing techniques in adults and children [RETIRED]

Year: 2000

Type: review

Abstract: Overview.Neurologists are frequently called upon to evaluate patients with vertigo and dizziness and, in some cases, to make sense of abnormal vestibular tests.Consequently, it is useful to have some familiarity with the methods used to test vestibular function.The vestibulo-ocular reflex (VOR) is a reflex that acts at short latency to generate eye movements that compensate for head rotations in order to preserve clear vision during locomotion.The VOR is the most accessible gauge of vestibular function.Evaluating the VOR requires application of a vestibular stimulus and measurement of the resulting eye movements.This report reviews the advantages and limitations of the methods of stimulating the vestibular system: caloric irrigation, rotational chair testing, and auto-rotational testing.Vestibular testing in children is given additional consideration because of the paucity of recent reviews on the topic.This report will not address eye movement recording techniques, the neurophysiology of the VOR, which is reviewed elsewhere, 1,2 or interpretation of nystagmus.Literature review.This evidence-based assessment was developed from a review of published articles obtained through the MEDLINE database of the National Library of Medicine.Relevant publications were rated by the strength of evidence according to a scheme approved by the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology (see Appendix 2). Bedside vestibular assessment.Not every dizzy patient needs quantitative vestibular testing.Clinical examination can provide some qualitative information about vestibular function (table 1).Patients with dizziness should be examined for nystagmus in the supine and lateral head positions as well as following the Dix-Hallpike maneuver.Spontaneous and gaze-evoked nystagmus may help localize the lesion in a patient with a suspected vestibular disorder.2,3 Peripheral vestibular nystagmus is often suppressed by visual fixation, but may be seen during funduscopic examination in the dark.Frenzel goggles have 10+ diopter lenses that prevent fixation, allowing vestibular nystagmus to be seen.Skew deviation and a head tilt suggest a unilateral disturbance in the otolith-ocular pathways.Shortly after unilateral (otolith) vestibular loss, patients often perceive vertical as being tilted 10 to 30 degrees toward the lesioned side.4,5 In time, this distortion diminishes, but in some cases it may be present even after vestibular compensation has taken place.Although it is not the purpose of this article to thoroughly review the clinical vestibular examination, recently there have been useful new developments worthy of mention.For detection of unilateral vestibular deficits, the head thrust sign, head-shaking nystagmus, and vibration-induced nystagmus can be helpful.The head thrust sign entails horizontal (yaw-plane) high-acceleration head thrusts, while the patient maintains gaze on the examiner.During this maneuver, one looks for a "catch up" saccade when the head is rapidly turned toward the lesioned side.6 Head-shaking nystagmus can also demonstrate vestibular aysmmetry.7 The head is vigorously turned back and forth horizontally with eyes closed for about 30 seconds, to "charge" the brainstem's velocity storage mechanism.1 Upon stopping and opening the eyes (preferably using Frenzel lenses), nystagmus usually beats away from the lesioned side; such nystagmus is absent in normal subjects.Tapping the head 8 or application of a 60-Hz vibration stimulus to the mastoid bone can also evoke horizontal nystagmus beating away from the side of the vestibular loss.9 Dynamic visual acuity testing is indicated for those patients suspected of having bilateral vestibular loss 10 ; abnormalities usually correlate with oscillopsia.Worsening of visual acuity by at least three lines on a visual acuity chart (e.g., Snellen chart or Rosenbaum card) during head turning from side to side at 1 Hz or more is abnormal.

Source: Neurology

DOI: 10.1212/wnl.55.10.1431