Horizontal head impulse test detects gentamicin vestibulotoxicity.
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 degrees-6,000 degrees/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 degrees/sec2 to 46% at 6,000 degrees/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.
Weber
K P
KP
Department of Neurology, Royal Prince Alfred Hospital, Sydney, Australia.
Aw
S T
ST
Todd
M J
MJ
McGarvie
L A
LA
Curthoys
I S
IS
Halmagyi
G M
GM
D000328:Adult; D000368:Aged; D005133:Eye Movements / Q000187:drug effects / Q000502:physiology; D005260:Female; D005839:Gentamicins / Q000009:adverse effects*; D019416:Head Movements / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009434:Neural Pathways / Q000503:physiopathology; D015835:Ocular Motility Disorders / Q000139:chemically induced* / Q000175:diagnosis* / Q000503:physiopathology; D009801:Oculomotor Muscles / Q000503:physiopathology; D019095:Point-of-Care Systems; D011237:Predictive Value of Tests; D011500:Protein Synthesis Inhibitors / Q000009:adverse effects; D012027:Reflex, Vestibulo-Ocular / Q000187:drug effects / Q000502:physiology; D012438:Saccades / Q000187:drug effects / Q000502:physiology; D012665:Semicircular Canals / Q000187:drug effects / Q000503:physiopathology; D015837:Vestibular Diseases / Q000139:chemically induced* / Q000175:diagnosis* / Q000503:physiopathology; D014724:Vestibular Function Tests / Q000379:methods*; D014722:Vestibule, Labyrinth / Q000187:drug effects / Q000503:physiopathology
D005839:Gentamicins; D011500:Protein Synthesis Inhibitors