Bone-Anchored Hearing Devices for Single-Sided Deafness: A New Preoperative Evaluation Protocol and Widening of Indications Proposal

Abstract

Introduction: Bone-anchored hearing devices (BAHD) are well-known good solution for single-sided deafness (SSD). Despite power extension of recently introduced BAHD with implanted active transducer, with indications up to 65 dB Hl of bone conduction (BC) threshold on the implanted side, their indications for SSD still remain better than 25 dB on the good ear, with regards to bone conduction thresholds. The aim of this study was to assess the possibility to enlarge BAHD indications for SSD by means of a newly proposed candidacy evaluation protocol, which includes a new software-aided method.

Methods: 20 SSD patients (mean age 56 years, 9 females, and 11 males) were divided into two groups: group A (10 patients, BC <25 dB Hl on the hearing side) and group B (10 patients, BC between 25 and 35 dB Hl). Recipients were submitted to bisyllabic words speech audiometry in silence and to authors' newly proposed IFastSRT50 test by means of software which shift noise intensity of a single word list on the basis of correct recipient recognition responses. A sound speaker for signal (bisyllabic words) and noise (babble) was disposed at 1 m from the deaf side of the patient. An earphone covering only the good ear of the recipient was used in order to perform its air conduction masking with white noise. A BAHD test device was disposed on the mastoid of the deaf side. Both signal and masking intensities were set to 55 dB SPL in order to mask airway conduction on the good ear without masking its bone way interaural conduction from the BAHD tester.

Results: With BAHD tester turned off, no recognition was detected. Speech audiometry with BAHD tester turned on revealed mean values of 92% for group A and 89% for group B, with a difference of 3.0% (χ2 = 0.285 and p = 0.5935). As for IFastSRT50 with BAHD tester turned on, mean signal-to-noise ratio value to obtain 50% of recognition was -6.89 for group A and -6, with a difference of 0.89 (t = 1,201 and p = 0.2453).

Conclusion: BAHD are confirmed to be a good solution for SSD cases. The absence of statistically significant differences in our two tested groups suggests that newer implanted active transducer device indications should be extended up to 35 dB Hl on the hearing ear. The IFastSRT50 is a reliable and quick method to enhance preoperative candidacy evaluation.

Keywords: Bone-anchored hearing devices; Signal-to-noise ratio; Single-sided deafness; Speech reception thresholds.