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Vibration-Induced Nystagmus: A simple test for peripheral vestibular asymmetry Authors Peter West, MA, MSc, BM, BCh, FRCS, FRCP Consultant Audiovestibular Physician Austin Timoney MSc Pre-registration Clinical Scientist

Introduction Vibration (60-100 Hz) applied to either mastoid process may provoke nystagmus in patients with unilateral peripheral vestibular hypofunction.Testing for Vibration-Induced Nystagmus (VIN) allows many cases of peripheral vestibular imbalance to be identified in the out-patient clinic in under a minute without recourse to expensive, time consuming and (in the case of caloric testing) unpleasant investigations. The VIN test has been in routine use in the first author’s Audiovestibular Medicine clinics for two years, where it has proved an invaluable aid to rapid diagnosis. But, although it is supported by an international literature dating to the late 1990s, it remains largely unknown and unused in the UK. This article aims to encourage its adoption in all clinics where significant numbers of dizzy or balance disordered patients are seen, to facilitate efficient and cost-effective diagnosis as part of the routine vestibular examination and test battery.

Figure 1: Synapsys Vestibular Vibrator

skull vibration to be alarming and even unpleasant. It is therefore recommended that the vibrator be demonstrated on the back of the patient’s hand before it is applied to the mastoid, to encourage their cooperation.

“The VIN test is an excellent clinical screening tool for unilateral or asymmetrical peripheral vestibular weakness” Figure 2: Performing the VIN test

Equipment Whilst the first author initially experimented (with some success) with a battery powered “massager” purchased from Argos for £10, the VIN test should be performed using a powerful mains-powered vibrator, preferably offering frequency specific vibration. At Queen Alexandra Hospital, a Synapsys Vestibular Vibrator (Figure 1) provides vibration at frequencies of 60 and 100 Hz. As the induced nystagmus is of peripheral origin and may therefore be suppressed by optic fixation, eye movements should be examined with fixation removed using infra-red video-Frenzel’s goggles (which should, in any case, be in routine use in all vestibular clinics (1)). VIN may also be recorded as part of the vestibular test battery using Electronystagmography (ENG) or Videonystagmography (VNG) equipment. Method Although even a positive test will induce little or no subjective vertigo, some patients find the sudden application of vigorous

The patient is seated wearing video-Frenzel’s goggles with fixation removed and is instructed to look straight ahead with eyes open for the duration of the test. Vibration is applied at 60 and 100 Hz, with firm pressure, to each mastoid process in turn for 10 seconds. The exact position is said not to be critical but the first author has had most success with the vibrator held level with the external auditory meatus (Figure 2) or to the mastoid tip. Alternatively, the vibrator may be applied to the lower part of the sternocleidomastoid muscle (taking care to avoid the carotid body) but this position has been found to be less effective. Interpretation A strength of the VIN test is that any vibration-induced nystagmus will begin immediately, persist for the duration of vibration and cease instantly when the vibrator is switched off. Hamann and Schuster (1999) found no adaptation of the

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