Toward Optimizing Cervical Vestibular Evoked Myogenic Potentials (cVEMP): Combining Air-Bone Gap and cVEMP Thresholds to Improve Diagnosis of Superior Canal Dehiscence

Abstract

This is the largest study to date examining the usefulness of cVEMPs in the diagnosis of SCD. Our "third window indicator" (TWI) combines cVEMP thresholds with the ABG at 250 Hz to improve the ability to screen patients with SCD symptoms.

Vestibular Evoked Myogenic Potential (VEMP) Testing for Diagnosis of Superior Semicircular Canal Dehiscence

“…In all studies, the ABGs, cVEMP thresholds, and normalized peak-to-peak amplitudes of the thin group were very similar to the healthy control group. No significant difference between the thin and healthy control group was found for any of these metrics (12,32,34). In the study investigating a clinical population in which all included patients were suspected of having SCD based on symptoms, none of the thin ears met the 2 kHz cVEMP criterion for SCD abnormality (34).…”

“…The cVEMP can reliably differentiate symptomatic patients with actual dehiscence from those with thin or normal bone covering the superior semicircular canal (12,32,34). As yet, there is no compelling explanation for clinical symptoms in those patients with thin bone on CT but normal cVEMP response.…”

“…This age effect was not observed in the dehiscent group and it seems that any age effect on cVEMP outcomes is overwhelmed in the presence of a dehiscence (32). The majority of SCD patients present in their 40s and 50s and although it may not be necessary to obtain different cutoff values within the most commonly studied age range (about 25-70 years old), these cutoff values should be used with caution in "extremes of age, " i.e., those younger than 25 and older than 70 years old (12,32).…”

“…Many, but not all, patients with SCDS suffer from low frequency air-bone gaps (ABG) of ≥10 dB, which can be due to low or negative bone-conduction thresholds and/or elevated air-conduction thresholds. The largest ABG is typically seen at 250 Hz (12). Obviously, ABGs are not unique to SCD.…”

“…ABGs and cVEMP thresholds were obtained at multiple frequencies and combining cVEMP thresholds and ABG from the same frequency, i.e., subtracting the ABG from the cVEMP threshold, increased positive predictive values at 250, 500, and 1,000 Hz (24). A later retrospective study including 142 SCD ears found that the difference in ABG between dehiscent and healthy control ears was largest at 250 Hz and showed that a calculation subtracting the 250 Hz ABG from the 500 Hz cVEMP threshold (dubbed the "Third Window Indicator") provided better classification between SCD and age-matched healthy controls, with a sensitivity of 82% and a specificity of 100%, compared to a 46% sensitivity, and 100% specificity for the 500 Hz cVEMP threshold alone (12). A smaller prospective study, also using an age-matched healthy control group, found the Third Window Indicator (TWI) to have an 88% sensitivity and 100% specificity [ Table 1; (32)].…”