Ankle Audiometry: A Clinical Test for the Enhanced Hearing Sensitivity for Body Sounds in Superior Canal Dehiscence Syndrome

Abstract

Introduction: The aim of this study was to develop a clinical test for body sounds' hypersensitivity in superior canal dehiscence syndrome (SCDS).

Method: Case-control study, 20 patients affected by SCDS and body sounds' hypersensitivity and 20 control matched subjects tested with a new test called ankle audiometry (AA). The AA consisted of a psychoacoustic hearing test in which the stimulus was substituted by a controlled bone vibration at 125, 250, 500, and 750 Hz, delivered at the medial malleolus by a steel spring-attached bone transducer prototype B250. For each subject, it was defined an index side (the other being non-index), the one with major symptoms in cases or best threshold for each tested frequency in controls. In 3 patients, the AA was measured before and after SCDS surgery.

Results: The AA thresholds for index side were significantly lower in SCDS patients (115.6 ± 10.5 dB force level [FL]) than in control subjects (126.4 ± 8.56 dB FL). In particular, the largest difference was observed at 250 Hz (-16.5 dB). AA thresholds in patients were significantly lower at index side in comparison with non-index side (124.2 ± 11.4 dB FL). The response obtained with 250 Hz stimuli outperformed the other frequencies, in terms of diagnostic accuracy for SCDS. At specific thresholds' levels (120 dB FL), AA showed relevant sensitivity (90%) and specificity (80%) for SCDS. AA did not significantly correlate to other clinical markers of SCDS such as the bone and air conducted hearing thresholds and the vestibular evoked myogenic potentials. The AA thresholds were significantly modified by surgical intervention, passing from 119.2 ± 9.7 to 130.4 ± 9.4 dB FL in 3 patients, following their relief in body sounds' hypersensitivity.

Conclusion: AA showed interesting diagnostic features in SCDS with significantly lower hearing thresholds in SCDS patients when compared to healthy matched subjects. Moreover, AA could identify the affected or more affected side in SCDS patients, with a significant threshold elevation after SCDS surgery, corresponding in body sounds' hypersensitivity relief. Clinically, AA may represent a first objective measure of body sounds' hypersensitivity in SCDS and, accordingly, be an accessible screening test for SCDS in not tertiary audiological centers.

Keywords: Autophony; B250; Hyperacusis; Superior canal dehiscence; Superior canal dehiscence syndrome.

Fig. 1

Test setting for AA. The B250 was placed in contact with the medial malleolus with a velcro band, with an adjusted tension corresponding to a pressure at contact point of 10 N. The subjects during testing wore hearing protection against air conducted hearing contamination and disposable foam ear tips in connection with audiometer to deliver masking noise to the not stimulated side ear.

Fig. 2

The frequency response in units of decibel root mean square relative 1 μ Newton per volt (dB RMS re 1 μN/V) for B250 (solid line), Minishaker (simple dashed line), and Radioear B81 (double dashed line) between 100 and 10,000 Hz normalized to 1 V RMS input voltage. The 31 dB difference at 250 Hz between B250 and Radioear B81 is highlighted [Fredén Jansson et al., 2021].

Fig. 3

Box plots indicating the AA distribution in the two groups (case/control). On Y axis, the value of AA given in dB FL; on X axis the four tested frequencies. The data were further sub-grouped relating to the index and non-index sides. o = outliers; x = extremes. Only significant between and within groups' differences related to the index side is shown with the relative level of significance (* <0.05; ** <0.01; *** <0.001); the within groups' differences in control group are expected significant but not shown, as a result of the assignment of index/non-index sides.

Fig. 4

Box plot: AA hearing lateralization in cases (a) and control subjects (b) for index and non-index sides. Chequered boxes indicate the ipsilateral responses, the white ones the responses referred centrally, and the striped ones the responses given contralaterally. b The centrally and contralaterally given responses show a ceiling effect.