Diagnostic Accuracy of Ocular Vestibular Evoked Myogenic Potentials for Superior Canal Dehiscence Syndrome in a Large Cohort of Dizzy Patients
Authors: Verrecchia Luca , Brantberg Krister , Tawfique Zheer , Maoli Duan 
Published: June 2018

Objectives:
To determine the diagnostic accuracy of ocular vestibular evoked myogenic potentials (oVEMPs) for superior canal dehiscence syndrome (SCDS) in a large cohort of unselected dizzy patients. Most SCDS patients are dizzy (90%); however, only 30% demonstrate archetypical SCDS clinical proxies (Tullio or Hennebert findings). Several case-control studies have addressed specific SCDS markers using VEMP testing, but the diagnostic value of VEMP for SCDS has not been demonstrated in a target population of dizzy patients. The aim of this study was to confirm the diagnostic properties of oVEMP for SCDS in an unselected cohort of dizzy patients.

Design:
This diagnostic accuracy study was performed in a tertiary referral center and included a consecutive sample of dizzy patients referred for vestibular function testing. One hundred fifty subjects were collected prospectively; five were excluded due to middle ear disorders, 10 had the target condition (SCDS group), and 135 had an alternative condition (non-SCDS group), based on diagnostic criteria for SCDS used in our department as reference standard. The non-SCDS group was subdivided into diagnostic categories including an “undefined dizziness” group. The index test applied to the total sample (missing data: 1%) consisted of oVEMP recording using three different stimulation modalities, that is, air-conducted (AC) sound stimulation and midsagittal bone-conducted (BC) vibration at both forehead (Fz) and vertex (Cz). Data analysis was conducted on four oVEMP parameters: amplitude, latency, amplitude asymmetry ratio, and interaural latency difference. Between-group analysis was conducted with nonparametric tests. The oVEMP diagnostic accuracy for SCDS was determined with uni/multiparametric receiver operating characteristic analysis. Best cutoff points were computed for those parameters or parameter combinations that showed an accuracy level appropriate for clinical use (area under the curve [AUC] > 0.8).

Results:
Different oVEMP parameters, in particular, the amplitude to AC stimulation (SCDS: 53, inter quartile range [IQR]: 27.6–68.3 µV; non-SCDS: 4.4, IQR: 2.0–8.1 µV; p < 0.001), were able to separate SCDS from non-SCDS conditions with statistical significance. AC oVEMP amplitude had the highest diagnostic accuracy (area under the curve = 0.96) for SCDS, with optimal sensitivity (100%) and high specificity (89%) at a specific cutoff point (16.7 µV); as an SCDS index, it could distinguish these patients not only from those with other vestibular diagnoses but also from patients with undefined dizziness (sensitivity 100%; specificity 81%).

Conclusions:
oVEMP was able to identify all subjects affected by SCDS, according to our diagnostic criteria, in a large cohort of unselected dizzy patients. The AC oVEMP amplitude parameter showed optimal sensitivity and high specificity for SCDS and may represent an ideal screening test for SCDS among dizzy patients. This is noteworthy when considering that not all SCDS patients express the clinical key features of vestibular hypersensitivity to sound or pressure change, even though most complain of dizziness.