Video head impulse test finding in vestibular lesions

Abstract

Introduction of video head impulse test (vHIT) as a new objective quantitative test of vestibular function, provides a new dimension in vestibular evaluation. 1vHIT is a simple fast clinical vestibular test. It has the ability to detect specific vestibular lesion by using physiologic high frequency stimuli and measure the gain of the vestibulo-occular reflex (VOR). If there is abnormal VOR response, the test can measure the gain of VOR and detect any refixation saccade (overt and covert saccades. 2The vestibular hair cells respond to frequencies from 0 to 16 Hz, being particularly active in the range of 0.1-10 Hz. The caloric test is usually in the area ranging from 0.003 to 0.05 Hz, but rotational tests are in the area of high frequencies. 3 The vHIT is a more physiological stimulus testing higher frequencies (>1Hz) Heuberger et al. 4 It is therefore possible that a subject may have a normal caloric test, but manifest VOR deficits during head movements within a higher frequency range. 5 Bartolomeo et al., 6 found the sensitivity of vHIT increased up to 86.7 % and specificity to 100 % when the caloric deficit is between 40 and 65 % in case of VN. The sensitivity of vHIT increased to 100 % if caloric deficit is more than 65.2 %. McCaslin et al., 7 found dissociation between caloric test and vHIT in MD as caloric tests showed a vestibular deficit, while the vHIT was normal in 45 % of the cases. Manzari et al., 8 reported an enhanced vHIT lateral canal gain response in all 13 Meniere's patients tested at attack and in 18 of 30 patients tested during quiescence. Their hypothesis was that the enlarged endolymph volume causes enhanced displacement and enhanced return of the cupula which might lead to enhanced response in MD patients.Caloric testing and the video head impulse test (vHIT) are reliable tests, caloric testing can evaluate the function of the lateral semicircular canal and superior vestibular nerve, However, vHIT can detect abnormalities in all six semicircular canals and it can be used in patients who do not tolerate caloric test such as some elder patient, children or patient with perforated tympanic membrane. 9 The vHIT can be used as a screening tool for vestibular deficits due to gentamicin toxicity. 10The simplicity of vHIT and its relatively innocuous character for patients means that it can be used even during vertigo attacks. So it has been used to show in patients with Menière's disease how semicircular canal function fluctuates during and around the time of the attack of vertigo Manzari et al. 8 Also there is need to have objective measure of the VOR during HIT by using a system fast enough and accurate enough to detect any type of saccades because some patients were missed by bedside head impulse test, even by expert examiners. 11 So this study is conducted to compare video head impulse test results among different vestibular lesions and healthy subjects and correlate between video head impulse test and caloric test results. MethodsThis study was carried out in the Audio vestibular unit at the A...