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Explore This IssueJune 2018
Head thrust tests initially were performed bedside to assess dizziness by clinically identifying eye movements associated with high-impulse passive head rotation. The Video Head Impulse Test (vHIT) measures the vestibulo-ocular reflex (VOR) and is anatomically correlated to semicircular canal function in the peripheral vestibular system, motor nuclei in the brainstem, and extraocular muscles. vHIT reveals vestibular hypofunction via measured gain reduction and the presence of covert or overt saccades. vHIT yields quick, objective results and has increased sensitivity compared to the clinical head impulse test (cHIT); measured covert saccades can be present even with central compensation and are often not detectable using cHIT. Debate exists regarding the utility of vHIT in the context of existing objective tests; in some cases, vHIT provides seemingly redundant diagnostic information. Of note, not all clinics may have access to equipment or adequately trained staff necessary to perform vHIT.
Caloric irrigation and rotary chair similarly utilize the VOR to identify lesions in the peripheral vestibular system. However, results from these tests also have been shown to dissociate, perhaps because vHIT and calorics evaluate the vestibular system in different frequency ranges. Dissociation in test findings may be related to changes in measurable vHIT results as compensation progresses, whereas the caloric asymmetry remains more stable. The goal of this article is to review recent literature to determine the clinical utility of vHIT in assessing a dizzy adult patient.
vHIT provides information complementary to other available vestibular tests and may be a key part of evaluating suspected peripheral vestibular deficits. It is quick, objective, and able to measure covert saccades and all six semicircular canals. If acute vestibular neuritis is in the differential but is not certain after initial history and physical exam, vHIT should be considered as part of the diagnostic workup. If vHIT proves to be abnormal in the acute setting, further vestibular testing is not necessary. For chronic patients, vHIT still is an appropriate first test. However, if after the acute phase the vHIT results normalize, caloric testing should be performed to rule out ongoing peripheral disease. Given the dissociation between vHIT and calorics for fluctuating vestibulopathies (e.g., VM or MD), the literature suggests preferentially doing caloric testing. For pathologies such as BPPV, vHIT adds minimal diagnostic value. More research is needed to further characterize vHIT results when following the progression of vestibular disease, as well as to enhance training and access to vHIT (Laryngoscope. 2017;127:2689–2690).