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NEUROLOGY 2009;72:1417-1424
© 2009 American Academy of Neurology

Horizontal head impulse test detects gentamicin vestibulotoxicity

K. P. Weber, MD, S. T. Aw, PhD, M. J. Todd, MBiomedE, L. A. McGarvie, MBiomedE, I. S. Curthoys, PhD and G. M. Halmagyi, MD

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 Central Clinical School (S.T.A.), Faculty of Medicine, 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: Parenteral antibiotic therapy with gentamicin, even in accepted therapeutic doses, can occasionally cause bilateral vestibular loss (BVL) due to hair cell toxicity.

Objective: To quantify in patients with gentamicin vestibulotoxicity (GVT) the extent of acceleration gain deficit of the horizontal vestibulo-ocular reflex at different accelerations with a graded head impulse test (HIT) in comparison with standard caloric and rotational testing. To characterize the corresponding HIT catch-up saccade pattern to provide the basis for its salience to clinicians.

Methods: Horizontal HIT of graded acceleration (750°–6,000°/sec2) was measured with binocular dual search coils in 14 patients with GVT and compared with 14 normal subjects and a control subject with total surgical BVL.

Results: Patients showed mostly symmetric HIT gain deficits with a continuous spectrum from almost normal to complete BVL. Gain deficits were present even at the lowest head accelerations. HIT gain correlated better with caloric (Spearman {rho} = 0.85, p = 0.0001) than rotational testing ({rho} = 0.55, p = 0.046). Cumulative amplitude of overt saccades after head impulses was 5.6 times larger in patients than in normal subjects. Compared with previously published patients after unilateral vestibular deafferentation, GVT patients with BVL generated only approximately half the percentage of covert saccades during head rotation (23% at 750°/sec2 to 46% at 6,000°/sec2).

Conclusions: Head impulse testing is useful for early bedside detection of gentamicin vestibulotoxicity because most patients, even those with partial bilateral vestibular loss (BVL), have large overt saccades. Covert saccades, which can conceal the extent of BVL, are only approximately half as frequent as in unilateral patients, but may be present even in total BVL.

Abbreviations: BVL = bilateral vestibular loss; CI = confidence interval; GVT = gentamicin vestibulotoxicity; HIT = head impulse test; UVD = unilateral vestibular deafferentation; VOR = vestibulo-ocular reflex.

Supplemental data at www.neurology.org

Supported by the Garnett Passe and Rodney Williams Memorial Foundation, National Health and Medical Research Council Australia, and Neurology Trustees Royal Prince Alfred Hospital.

Disclosure: The authors report no disclosures.

Received September 14, 2008. Accepted in final form January 5, 2009.




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H. G. MacDougall, K. P. Weber, L. A. McGarvie, G. M. Halmagyi, and I. S. Curthoys
The video head impulse test: Diagnostic accuracy in peripheral vestibulopathy
Neurology, October 6, 2009; 73(14): 1134 - 1141.
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