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      The Video Head Impulse Test (vHIT) Detects Vertical Semicircular Canal Dysfunction

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          Abstract

          Background

          The video head impulse test (vHIT) is a useful clinical tool to detect semicircular canal dysfunction. However vHIT has hitherto been limited to measurement of horizontal canals, while scleral search coils have been the only accepted method to measure head impulses in vertical canals. The goal of this study was to determine whether vHIT can detect vertical semicircular canal dysfunction as identified by scleral search coil recordings.

          Methods

          Small unpredictable head rotations were delivered by hand diagonally in the plane of the vertical semicircular canals while gaze was directed along the same plane. The planes were oriented along the left-anterior-right-posterior (LARP) canals and right-anterior-left-posterior (RALP) canals. Eye movements were recorded simultaneously in 2D with vHIT (250 Hz) and in 3D with search coils (1000 Hz). Twelve patients with unilateral, bilateral and individual semicircular canal dysfunction were tested and compared to seven normal subjects.

          Results

          Simultaneous video and search coil recordings were closely comparable. Mean VOR gain difference measured with vHIT and search coils was 0.05 (SD = 0.14) for the LARP plane and −0.04 (SD = 0.14) for the RALP plane. The coefficient of determination R 2 was 0.98 for the LARP plane and 0.98 for the RALP plane and the results of the two methods were not significantly different. vHIT and search coil measures displayed comparable patterns of covert and overt catch-up saccades.

          Conclusions

          vHIT detects dysfunction of individual vertical semicircular canals in vestibular patients as accurately as scleral search coils. Unlike search coils, vHIT is non-invasive, easy to use and hence practical in clinics.

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          Most cited references15

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          A clinical sign of canal paresis.

          G M Halmagyi, I S Curthoys (1988)
          Unilateral loss of horizontal semicircular canal function, termed canal paresis, is an important finding in dizzy patients. To our knowledge, apart from head-shaking nystagmus, no clinical sign of canal paresis has yet been described and the term derives from the characteristic finding on caloric tests: little or no nystagmus evoked by either hot or cold irrigation of the affected ear. We describe a simple and reliable clinical sign of total unilateral loss of horizontal semicircular canal function: one large or several small oppositely directed, compensatory, refixation saccades elicited by rapid horizontal head rotation toward the lesioned side. Using magnetic search coils to measure head and eye movement, we have validated this sign in 12 patients who had undergone unilateral vestibular neurectomy.
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            The video head impulse test: diagnostic accuracy in peripheral vestibulopathy.

            H G Macdougall, K. P. Weber, L A McGarvie … (2009)
            The head impulse test (HIT) is a useful bedside test to identify peripheral vestibular deficits. However, such a deficit of the vestibulo-ocular reflex (VOR) may not be diagnosed because corrective saccades cannot always be detected by simple observation. The scleral search coil technique is the gold standard for HIT measurements, but it is not practical for routine testing or for acute patients, because they are required to wear an uncomfortable contact lens. To develop an easy-to-use video HIT system (vHIT) as a clinical tool for identifying peripheral vestibular deficits. To validate the diagnostic accuracy of vHIT by simultaneous measures with video and search coil recordings across healthy subjects and patients with a wide range of previously identified peripheral vestibular deficits. Horizontal HIT was recorded simultaneously with vHIT (250 Hz) and search coils (1,000 Hz) in 8 normal subjects, 6 patients with vestibular neuritis, 1 patient after unilateral intratympanic gentamicin, and 1 patient with bilateral gentamicin vestibulotoxicity. Simultaneous video and search coil recordings of eye movements were closely comparable (average concordance correlation coefficient r(c) = 0.930). Mean VOR gains measured with search coils and video were not significantly different in normal (p = 0.107) and patients (p = 0.073). With these groups, the sensitivity and specificity of both the reference and index test were 1.0 (95% confidence interval 0.69-1.0). vHIT measures detected both overt and covert saccades as accurately as coils. The video head impulse test is equivalent to search coils in identifying peripheral vestibular deficits but easier to use in clinics, even in patients with acute vestibular neuritis.
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              Head impulse test in unilateral vestibular loss: vestibulo-ocular reflex and catch-up saccades.

              K. P. Weber, S Aw, M. Todd … (2008)
              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. To determine the VOR deficit and catch-up saccade characteristics in unilateral vestibular disease in response to HIT of varying accelerations. 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). 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 degrees /sec(2), 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. 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.
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                Author and article information

                Contributors
                Matthew Thurtell: Role: Editor
                Journal
                Journal ID (nlm-ta): PLoS One
                Journal ID (iso-abbrev): PLoS ONE
                Journal ID (publisher-id): plos
                Journal ID (pmc): plosone
                Title: PLoS ONE
                Publisher: Public Library of Science (San Francisco, USA )
                ISSN (Electronic): 1932-6203
                Publication date Collection: 2013
                Publication date (Electronic): 22 April 2013
                Volume: 8
                Issue: 4
                Electronic Location Identifier: e61488
                Affiliations
                [1 ]Vestibular Research Laboratory, School of Psychology, University of Sydney, Sydney, Australia
                [2 ]Department of Neurology, Royal Prince Alfred Hospital, Sydney, Australia
                [3 ]Department of Ophthalmology, University Hospital Zurich, Zurich, Switzerland
                [4 ]Department of Neurology, University Hospital Zurich, Zurich, Switzerland
                University of Iowa, United States of America
                Author notes

                Competing Interests: All authors have acted as unpaid consultants and have received funding for travel and free equipment for beta testing from GN Otometrics. However, the study was conducted with a custom-built, noncommercial prototype and the authors have no commercial interest in video head impulse systems. This does not alter their adherence to all the PLOS ONE policies on sharing data and materials.

                Revision of manuscript: HGM LAM GMH. Interpretation of data: HGM LAM GMH ISC KPW. Statistics: HGM ISC. Conceived and designed the experiments: HGM ISC KPW. Performed the experiments: HGM LAM GMH KPW. Analyzed the data: HGM ISC. Contributed reagents/materials/analysis tools: LAM KPW. Wrote the paper: ISC KPW.

                Article
                Publisher ID: PONE-D-13-00870
                DOI: 10.1371/journal.pone.0061488
                PMC ID: 3632590
                PubMed ID: 23630593
                SO-VID: 769f6f34-2a59-4238-8fc1-e0f63cf05fb3
                Copyright statement: Copyright @ 2013
                License:

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                Date received : 28 December 2012
                Date accepted : 8 March 2013
                Page count
                Pages: 10
                Funding
                This work was supported by the Garnett Passe and Rodney Williams Memorial Foundation, the National Health and Medical Research Council of Australia (grant number 632746) and the Betty and David Koetser Foundation for Brain Research. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Subject: Research Article
                Subject: Biology
                Subject: Anatomy and Physiology
                Subject: Neurological System
                Subject: Motor Systems
                Subject: Sensory Physiology
                Subject: Medicine
                Subject: Diagnostic Medicine
                Subject: Clinical Neurophysiology
                Subject: Test Evaluation
                Subject: Neurology
                Subject: Otorhinolaryngology
                Subject: Otology
                Subject: Vertigo

                ScienceOpen disciplines: Uncategorized
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                ScienceOpen disciplines: Uncategorized

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