Toward Optimizing cVEMP: 2,000-Hz Tone Bursts Improve the Detection of Superior Canal Dehiscence

Abstract

Background: The cervical vestibular evoked myogenic potential (cVEMP) test measures saccular and inferior vestibular nerve function. The cVEMP can be elicited with different frequency stimuli and interpreted using a variety of metrics. Patients with superior semicircular canal dehiscence (SCD) syndrome generally have lower cVEMP thresholds and larger amplitudes, although there is overlap with healthy subjects. The aim of this study was to evaluate which metric and frequency best differentiate healthy ears from SCD ears using cVEMP.

Methods: Twenty-one patients with SCD and 23 age-matched controls were prospectively included and underwent cVEMP testing at 500, 750, 1,000 and 2,000 Hz. Sound level functions were obtained at all frequencies to acquire threshold and to calculate normalized peak-to-peak amplitude (VEMPn) and VEMP inhibition depth (VEMPid). Third window indicator (TWI) metrics were calculated by subtracting the 250-Hz air-bone gap from the ipsilateral cVEMP threshold at each frequency. Ears of SCD patients were divided into three groups based on CT imaging: dehiscent, thin or unaffected. The ears of healthy age-matched control subjects constituted a fourth group.

Results: Comparing metrics at all frequencies revealed that 2,000-Hz stimuli were most effective in differentiating SCD from normal ears. ROC analysis indicated that for both 2,000-Hz cVEMP threshold and for 2,000-Hz TWI, 100% specificity could be achieved with a sensitivity of 92.0%. With 2,000-Hz VEMPn and VEMPid at the highest sound level, 100% specificity could be achieved with a sensitivity of 96.0%.

Conclusion: The best diagnostic accuracy of cVEMP in SCD patients can be achieved with 2,000-Hz tone burst stimuli, regardless of which metric is used.

Keywords: Cervical vestibular evoked myogenic potential; Superior canal dehiscence; Vestibular nerve function.

Fig. 1.

a Average air-bone gap (ABG) at 250 Hz for each group. Error bars represent 95% confidence intervals. The ABG was significantly higher for the dehiscent group (asterisk) compared to thin, unaffected and healthy-control groups. There were no significant differences among unaffected, thin and healthy-control ears. b Average cVEMP threshold tuning relative to the 750-Hz threshold. As can be appreciated visually, the dehiscent-ear tuning curve is flatter than the healthy-ear tuning curve.

Fig. 2.

Average cVEMP threshold (a) and third window indicator (TWI) (b) for 500, 750, 1,000 and 2,000 Hz. Error bars represent the 95% confidence intervals. Both cVEMP thresholds and the TWI were significantly lower in the dehiscent group compared to the thin, unaffected and healthy-control groups.

Fig. 3.

Top: average normalized peak-to-peak amplitude (VEMPn). Bottom: average VEMP inhibition depth (VEMPid). Data from 500 (a, e), 750 (b, f), 1,000 (c, g) and 2,000 Hz (d, h) for multiple sound levels. Error bars represent 95% confidence intervals. The effect of frequency is significantly larger at the higher sound levels, and the effect of stimulus level is significantly larger in the dehiscent group compared to the other groups.

Fig. 4.

Receiver-operating characteristic curves displaying sensitivity of detecting a dehiscence versus false positive rate (1 – specificity) for cVEMP thresholds (a) and third window indicators (TWIs) (b) for 500, 750, 1,000 and 2,000 Hz. Insets show the frequency key and the corresponding area under the curve (AUC). cVEMP threshold and TWI data have 5-dB steps so that normal and affected subjects can have the same threshold. Thus, a change in cutoff value can produce a change in both the sensitivity and specificity at once, which causes points to be connected by diagonal lines.

Fig. 5.

Receiver-operating characteristic (ROC) curves displaying sensitivity of detecting a dehiscence versus false positive rate (1 – specificity) for normalized peak-to-peak amplitude (VEMPn) (top row) and VEMP inhibition depth (VEMPid) (bottom row) for 500, 750, 1,000 and 2,000 Hz at multiple sound levels. Insets show the frequency key and the corresponding area under the curve (AUC).