New, fast, clinical vestibular tests identify whether a vertigo attack is due to early Ménière's disease or vestibular neuritis

INTRODUCTION When a patient arrives at a clinic with an acute attack of vertigo, a major question facing the clinician is what is the cause of this attack? Is it due to early M enière’s disease (MD) or due to vestibular neuritis (VN)? Both cause severe attacks with vertigo and nystagmus, but the treatment and therapeutic progression and the outcomes for these two causes are entirely different. How is it possible to distinguish between them? The history may be indefinite. The direction of spontaneous nystagmus can be misleading because in some early MD cases the quick phase of the nystagmus beats toward the affected ear. Caloric testing gives evidence about the level of horizontal canal function, but the variability of the caloric test is high and giving a caloric test to a patient in the midst of a major attack of vertigo is difficult and distressing for both the patient and the clinician, and many such patients refuse to undergo a caloric test, or worse still, do not complete the test. Here we report the results of two patients with very similar vertigo attacks to show how, by applying new clinical tests, it is possible to distinguish simply and quickly between an attack due to early MD as opposed to VN in a way that is fast and not distressing for the patient (or the clinician). The first test is the video head impulse test (vHIT), which measures the eye movement response to brief, passive, unpredictable, small, horizontal head turns with values of angular acceleration in the range encountered in natural head movements. A headmounted video camera measures both the eye movement and the head velocity, and software quantifies the vestibulo-ocular reflex (VOR) gain during the brief head turns to the left and right. In this way, vHIT provides an objective measure of physiological horizontal semicircular canal function. VN causes reduced horizontal VOR gain for head turns to the affected side, whereas in MD at attack, horizontal VOR gain for head turns to the affected side is normal or even enhanced. Because only about 20 small head turns are required (lasting in total about 2 minutes), patients even in the midst of a major vertigo attack are, in our experience, not troubled by this vHIT test. It is far quicker and far less distressing than a full caloric test, and it provides measures of the slow phase eye velocity even with a vigorous ongoing nystagmus. The second test is the ocular vestibular evoked myogenic potential (oVEMP), which is recorded by surface electrodes on the skin just beneath the eyes as the patient looks up, in response to bone-conducted vibration (BCV) (500 Hz) delivered at the junction of the midline at the hairline (a location called Fz). There is now considerable evidence that the first component of the oVEMP—a negative potential at a latency of around 10 ms from stimulus onset (oVEMP n10)—is a crossed myogenic response indicating otolithic and utricular function of the ear opposite the recorded eye. In unilateral vestibular neuritis, the oVEMP n10 response is reduced or absent beneath the eye opposite the affected ear, whereas the n10 beneath the eye on the side of the From the MSA ENT Academy Center (L.M.), Cassino, Italy; and the Vestibular Research Laboratory (H.G.M., A.M.B., I.S.C.), School of Psychology, the University of Sydney, New South Wales, Australia. Editor’s Note: This Manuscript was accepted for publication May 10, 2012. Emeritus Professor Ian Curthoys is funded by project grants from the National Health and Medical Research Council of Australia and the Garnett Passe and Rodney Williams Memorial Foundation. He is also an unpaid consultant to GN Otometrics, Taastrup, Denmark. Dr. Ann Burgess and Dr. Hamish G. MacDougall are funded by a project grant from the National Health and Medical Research Council of Australia and the Garnett Passe and Rodney Williams Memorial Foundation, respectively. Dr. Hamish G. MacDougall is also an unpaid consultant to GN Otometrics, Taastrup, Denmark. The authors have no other funding, financial relationships, or conflicts of interest to disclose. Send correspondence to Ian S. Curthoys, PhD, Vestibular Research Laboratory, School of Psychology, A18, University of Sydney, Sydney, NSW 2006, Australia. E-mail: ianc@psych.usyd. edu.au