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Head impulse test in unilateral vestibular loss

Vestibulo-ocular reflex and catch-up saccades

From the Department of Neurology (K.P.W., S.T.A., M.J.T., L.A.M., G.M.H.), Royal Prince Alfred Hospital, Sydney; and Vestibular Research Laboratory (I.S.C.), School of Psychology, University of Sydney, Australia.

Address correspondence and reprint requests to Dr. G. Michael Halmagyi, Neurology Department, Royal Prince Alfred Hospital, Camperdown NSW 2050, Sydney, Australia michael{at}icn.usyd.edu.au

Background: Quantitative head impulse test (HIT) measures the gain of the angular vestibulo-ocular reflex (VOR) during head rotation as the ratio of eye to head acceleration. Bedside HIT identifies subsequent catch-up saccades after the head rotation as indirect signs of VOR deficit.

Objective: To determine the VOR deficit and catch-up saccade characteristics in unilateral vestibular disease in response to HIT of varying accelerations.

Methods: Eye and head rotations were measured with search coils during manually applied horizontal HITs of varying accelerations in patients after vestibular neuritis (VN, n = 13) and unilateral vestibular deafferentation (UVD, n = 15) compared to normal subjects (n = 12).

Results: Normal VOR gain was close to unity and symmetric over the entire head-acceleration range. Patients with VN and UVD showed VOR gain asymmetry, with larger ipsilesional than contralesional deficits. As accelerations increased from 750 to 6,000 °/sec², ipsilesional gains decreased from 0.59 to 0.29 in VN and from 0.47 to 0.13 in UVD producing increasing asymmetry. Initial catch-up saccades can occur during or after head rotation. Covert saccades during head rotation are most likely imperceptible, while overt saccades after head rotation are detectable by clinicians. With increasing acceleration, the amplitude of overt saccades in patients became larger; however, initial covert saccades also became increasingly common, occurring in up to about 70% of trials.

Conclusions: Head impulse test (HIT) with high acceleration reveals vestibulo-ocular reflex deficits better and elicits larger overt catch-up saccades in unilateral vestibular patients. Covert saccades during head rotation, however, occur more frequently with higher acceleration and may be missed by clinicians. To avoid false-negative results, bedside HIT should be repeated to improve chances of detection.

Abbreviations: HIT = head impulse test; UVD = unilateral vestibular deafferentation; VN = vestibular neuritis; VOR = vestibulo-ocular reflex.

Supplemental data at www.neurology.org

Supported by the Garnett Passe and Rodney Williams Memorial Foundation.

Disclosure: The authors report no conflicts of interest.

Received May 23, 2007. Accepted in final form August 6, 2007.