Video Head Impulse Test (vHIT) and Vestibular Evoked Myogenic Potential (VEMP) Test for Assessment of Vertigo: Our Initial Experience

Introduction: Loss of balance causes the sensation of vertigo. Balance is maintained by vestibular afferent from labyrinth, eyes and proprioceptors and their central integration. For diagnosis of vertigo, along with history different vestibulometric tests can be done to identify the specific anatomical part that is involved. Material and methods: A cross sectional study was done among 82 patients who did video Head Impulse Test (vHIT) and among 75 patients who did Vestibular Evoked Myogenic Potential (VEMP) test at AudiovestibularCentre(AVC) at Bangladesh ENT Hospital Ltd. during the period from April 2018 to September 2019. Results: Age range of the sample was 16 to 80 years. Among the 82 patients who did vHIT 62(75.6%) had abnormality in either Semi Circular Canal. Among 75 patients who did VEMP 27(36%) were detected to have abnormality in either in saccule or utricle. Conclusion: For diagnosis of cause of vertigo the appropriate test for individual part of vestibule is essential. vHIT and VEMP are two tests which are complementary to each other in explaining common peripheral causes of vertigo.


Introduction:
According to 1995 guidelines by the American Academy of Otolaryngology-Head and Neck Surgery, vertigo is characterized as ''the sensation of motion when no motion is occurring relative to earth's gravity. ''1 Vertigo can disrupt a person's daily activities and have a profoundly negative impact on his or her quality of life. 2,3 The balance system serves three primary functions namely i. maintenance of posture stability -for standing comfortably and prevention from falling, ii. Perception of subjective visual vertical and horizontal -for spatial orientation of an object with respect to gravity, iii. Gaze stabilization or visual stability -so that objects in the visual field remain stable and do not appear to be moving when the head is moved, or when the visual surroundings move, or when both the head and the visual surroundings move.
Vestibular afferent from labyrinth, eyes and proprioceptors execute their function through effererent motor organs through vestibuloocular reflex (VOR), vestibulocollicreflex(VCR) and vesibulospinal reflex (VSR). For diagnosis of patients presented with with dizziness, vertigo, taking history from the patient is of utmost importance and different vestibulometric tests are now also available to identify the specific anatomical part that is involved.
The video head impulse test (vHIT) incorporates a new technology that uses a pair of high-speed, light-weight video goggles to measure (left or right) eye velocity in response to head movement and record "catch-up" saccades (and other abnormalities) in patients with an impaired VOR.
vHIT provides a quick and objective measure of the VOR in response to head movements in the natural range of daily motions and thus evaluates the functional integrity of all the six Semi Circular Canals (SCC)s of bothsides ( Fig.1,2,3).Hence, this test is much more relevant than the caloric ENG/ VNG tests. Vestibular evoked myogenic potentials (VEMPs) are becoming widely used for detailed neurophysiological assessment of the vestibular system. A VEMP is basically a myogenic response from the muscles of the neck or eyes, in response to loud acoustic stimulation of the otolith organs(viz., the saccule and utricle). 4 Ocular VEMPs (oVEMPs) (Fig. 4) measure the function of the vestibulo-ocular reflex arc (utricle, superior vestibular nerve, brainstem vestibular nuclei, medial longitudinal fasciculus, inferior oblique muscle) 5 . Cervical VEMPs (cVEMPs) (Fig.5) measure the integrity of the vestibulo-collic reflex (saccular afferents, inferior vestibular nerve, the brainstem vestibular nuclei, the medial vestibulospinal tract, upper cervical motor neurons and the accessory nerve) 5 .

Materials and Methods:
A cross sectional study was done among 82 patients who were referred for video Head Impulse Test (vHIT) and among 75 patients who did Vestibular Evoked Myogenic Potential (VEMP) test during the period from April 2018 to September 2019. All the tests were done in AudiovestibularCentre(AVC) at Bangladesh ENT Hospital Ltd. vHIT is done by Eye See Cam of Interacoustics and VEMP tests are done by protocol of Eclipse by Interacoustics.

Results:
Age range of the sample was 16 to 80 years. Among the 82 patients who did vHIT 62(75.6%) had abnormality in either SCC. Among 75 patients who did VEMP 27(36%) were detected to have abnormality in either in saccule or utricle.

Discussion:
The central and peripheral vestibular system, in conjunction with the ocular and somatosensory system, is responsible for equilibrium balance and orientation in the space. Of all the symptoms of otological/ neurotological diseases vertigo can be one of the most incapacitating of symptoms.
A detailed history, clinical examination, neurological examination is mandatory in assessment of a dizzy patient. With advancement of computer aided neurotological investigation we can locate the more accurately the site of lesion. Table I shows among the referred patients about two-third (~64%) belonged to 41-70 years of age range. It represent the referral pattern in this series but Prevalence of dizziness increases significantly with age and among institutionalized patients 6 .   it is obvious that the combined use of VEMPs and vHIT we can analyze the peripheral vestibular function to far greater detail than by only using the caloric test 9 .

Conclusion:
Vertigo almost always arises from the vestibule and rarely from central or intracranial causes. Approximately 80% of vertigo cases result from peripheral causes, including Meniere's disease, vestibular neuritis, and benign paroxysmal positional vertigo. Central-type vertigo is caused by more severe diseases, including migrainous vertigo, brainstem ischemia, cerebellar infarction, and intracranial hemorrhage. 10 So for identification of the part of the vestibule involved, the appropriate test for individual part is an essential key to diagnosis. vHIT and VEMP are two tests which are complementary to each other in explaining common peripheral causes of vertigo.