Skull Vibration-Induced Nystagmus and High Frequency Ocular Vestibular-Evoked Myogenic Potentials in Superior Canal Dehiscence

Abstract

Background: Although diagnostic criteria have been established for superior canal dehiscence syndrome, cases in which the diagnosis is not easy are frequent. On those occasions, some tests such as vibration-induced nystagmus or vestibular-evoked myogenic potentials can offer invaluable help due to their high sensitivity and specificity. Methods: We studied 30 patients showing superior canal dehiscence or “near-dehiscence” in a CT scan. Skull vibration-induced nystagmus and high frequency ocular vestibular-evoked myogenic potentials are performed in each patient. The aim of the study is to determine how useful both tests are for detection of superior canal dehiscence or near-dehiscence. Results: Of the 60 temporal bones studied, no dehiscence was the result in 22, near-dehiscence in 17 and a definite finding in 21. In 10/30 patients, there was no SVIN (Skull vibration induced nystagmus) during otoneurological testing, while in 6/30, induced nystagmus was mainly horizontal, and in 14/30 there was vertical up-beating. All patients had a positive oVEMP (Ocular vestibular evoked myiogenic potentials) at 0.5 kHz in both ears and the HFoVEMP (High frequency ocular vestibular evoked myiogenic potentials) response was positive in 25/60 (41.6%) of the ears studied and in 19/30 of the patients evaluated (in 6 it was positive in both ears). Up-beat SVIN will point to a SCD (Superior Canal Dehiscence) mainly when HFoVEMP are present, and when this is negative there is a high probability that it is not a SCD. Conclusions: When SVIN and HFoVEMP results are added (or combined), they not only improve the possibilities of detecting SCD, but also the affected side.

A Single Fast Test for Semicircular Canal Dehiscence – oVEMP n10 to 4000Hz – Depends on Stimulus Rise-time

“…Studies of the 4000Hz test in SCD patients have used a variety of rise-times including some very long rise-times -even 4ms as used in the Lin et al study [20]). Tran et al [19] and Batuecas-Caletrio et al [14] both used 2ms and our data indicate that with such risetimes it is likely that there would be no detectable oVEMP n10 in some patients. We consider that the lower sensitivity and specificity values for the 4000Hz test may have been due in part to the fact that they did not use an optimum rise-time for the 4000Hz stimulus.…”

“…Others have confirmed the high specificity and sensitivity of high frequency stimuli to be a very effective way of identifying SCD [14,17,19]. However there have been some reports where the measured specificity and sensitivity of the 4000Hz test for SCD has been lower than what Manzari et al found [19,20].…”

“…That is why the use of 4000Hz to identify SCD was developed. (Variants of that 4000Hz test are now referred to as "high frequency VEMPs " [14]). A method with few stimulus presentations is to be preferred, and in 2013 we reported that a single test consisting of just 50 presentations of a 4000Hz stimulus, either BCV or ACS had excellent diagnostic accuracy.…”

A Single Fast Test for Semicircular Canal Dehiscence—oVEMP n10 to 4000 Hz—Depends on Stimulus Rise Time

“…Other authors have confirmed the high specificity and sensitivity of high frequency stimuli to be a highly effective way of identifying SCD [ 14 , 17 , 19 ]. However, there have been some reports where the measured specificity and sensitivity of the 4000 Hz test for SCD has been lower than what was found by Manzari et al [ 19 , 20 ].…”

“…The ideal diagnostic indicator would be a stimulus, in which healthy subjects have an extremely poor or absent response. In the interim, it has been reported that many phenomena apart from semicircular canal dehiscence can cause enhanced oVEMP n10 to 500 Hz stimulation (e.g., even intracochlear schwannoma [ 13 ]), and thus, the amplitude of the response to 500 Hz is not specific for SCD, which is why the use of 4000 Hz to identify SCD was developed (variants of the 4000 Hz test are now referred to as “high frequency VEMPs“ [ 14 ]). A method with few stimulus presentations is preferred, and in 2013, we reported that a single test consisting of only 50 presentations of 4000 Hz stimuli, BCV or ACS, had excellent diagnostic accuracy.…”