Vestibular-evoked myogenic potentials in the diagnosis of superior canal dehiscence syndrome

Patients with superior canal dehiscence (SCD) syndrome have vertigo and osc illopsia induced by loud noises and by stimuli that result in changes in mi ddle car or intracranial pressure. We recorded vestibular-evoked myogenic p otentials (VEMP responses) in 10 patients with SCD syndrome. The diagnosis had been confirmed in each case by evoked eye movements and by high-resolut ion CT scans of the temporal bones that showed a dehiscence overlying the a ffected superior canal. For the 8 patients without prior middle ear disease , the VEMP threshold from the dehiscent ears measured 72 +/- 8 dB NHL (norm al hearing level) whereas the threshold from normal control subjects was 96 +/- 5 dB NHL (p < 0.0001). The VEMP threshold measured from the contralate ral car in patients With unilateral dehiscence was 98 +/- 4 dB NHL (p > 0.9 with respect to normal controls). Two patients with apparent conductive he aring loss from middle ear disease, and SCD, had VEMP responses from the af fected ears. In the absence of dehiscence, VEMP responses would not have be en expected in the setting of conductive hearing loss. These findings confi rm earlier studies demonstrating that patients with SCD syndrome have lower ed VEMP thresholds. Conditions other than SCD syndrome may also lead to low ered VEMP thresholds. Rather than being based upon a single test, the diagn osis of SCD syndrome is best established when the characteristic symptoms, signs, VEMP response, and CT imaging all indicate SCD.