The Head Impulse Test in the Screening of Vestibular Function

The alternate binaural bithermal caloric test (ABBT) is a well established examination in the evaluation of the dizzy patient. ABBT is useful in detecting the side of peripheral vestibulopathy by stimulating each ear separately, it contributes to the diagnosis of bilateral vestibular involvement when all responses to cold and warm stimuli are reduced, and adds to the differentiation of peripheral from central vestibular involvement by measuring the fixation-induced inhibition of the caloric response. In spite of these benefits, ABBT is the most time-consuming part of the electronystagmography/Videonystagmography (ENG/VNG) test battery, and frequently causes significant inconvenience to the patient due to the repeated extreme vestibular stimuli. The head impulse test (HIT) assesses vestibular function by brisk, passive rotations of the head in the plane of the examined semicircular canals. Whenever the vestibulo-ocular reflex (VOR) is deficient, this maneuver would produce catch-up saccades aiming to the re-fixation of the eyes on the target. Hence, both residual VOR and catch-up saccades act synergistically to stabilize gaze. The HIT requires only several minutes and might cause minimal discomfort only. The study hypothesis is that the HIT recorded by standard VNG equipment of the VNG system would provide diagnostic information on the side of vestibular involvement matching that of the ABBT.