Vestibular evoked myogenic potentials in patients with superior semicircular canal dehiscence.

OBJECTIVE: To compare the audiometric and cervical vestibular evoked muscle potential (cVEMP) outcomes of ears with superior canal dehiscence (SSCD) to outcomes from normal ears and the unaffected ears of unilateral SSCD patients.

STUDY DESIGN: Retrospective review of clinical testing outcomes.

SETTING: Tertiary care specialty teaching hospital.

PATIENTS: Three subject groups were used: 21 ears of healthy subjects, ages 21 to 52 years; 58 affected SSCD ears in patients, ages 15 to 65 years; and 26 unaffected ears of unilateral SSCD patients, ages 15 to 65 years.

MAIN OUTCOME MEASURE: Results of pure-tone audiometry and cervical vestibular evoked muscle potential (cVEMP) testing.

RESULTS: SSCD ears differed from normal ears or unaffected ears of unilateral SSCD patients in 2 ways: 1) they had significantly larger air-bone gaps at 250 and 500 Hz, resulting in poorer air-conduction thresholds at those frequencies, and 2) their cVEMP thresholds at 500 Hz were significantly lower. When the cVEMP threshold was adjusted for the size of the air-bone gap on the audiogram, cVEMP thresholds were significantly lower for 250-, 500-, and 1,000-Hz tone bursts compared with the other subject groups. Logistic regression indicated that the probability of predicting SSCD from the cVEMP thresholds was significant. cVEMP tuning was unaffected by SSCD.

CONCLUSION: Combining 2 features associated with SSCD, the presence of an air-bone gap and the lower cVEMP threshold, into one variable, an adjusted cVEMP threshold, better separated SSCD ears from normal or unaffected SSCD ears. A probability predictive function from logistic regression of the adjusted cVEMP may be clinically applicable.