gms | German Medical Science

Introduction: The adequate treatment of the patients with moderate to severe mixed hearing loss (MHL) is not sufficiently possible with conventional hearing aids. These patients have enough cochlear reserve, but the additional middle ear disorder limits the usage of conventional hearing aids (gain limitation and distortion). The second possibility for such patients would be the bone conduction hearing aids, which indicate an insufficient gain for moderate to severe MHL. On the other hand because of good cochlear reserve there isn’t an indication for cochlear implantation. Therefore there is no optimal way to give an adequate gain to patients with moderate to severe MHL.

Method and patients: The newly-developed implantable DACS-System (Direct Acoustic Cochlear Stimulation) makes possible a direct coupling to the inner ear so that the problems of sound transfer in the middle ear can be circumvented. The conceptual hearing device is being employed in the first applied observation for patients with advanced Otosclerosis with a moderate to severe hearing loss. In such case parallel to a conventional stapes surgery (Stapedectomy) a second stapes prosthesis, driven through an artificial active incus, is placed. Figure 1 [Fig. 1] shows a schematic demonstration of DACS surgery.

In the frame of a multi-centered clinical study, four patients in Inselspital Bern and Medical University of Hanover were implanted with percutaneous DACS systems (the first 3 patients were implanted in Inselspital Bern, Switzerland). All patients were diagnosed with advanced Otosclerosis. None of the patients had had prior surgeries on the affected ear. All patients showed little to no hearing benefit with conventional hearing aids. Audiological examination consisted of routine pure tone audiometry (air and bone conduction), free-field audiometry with warble tone (in occlusion of the contralateral side), SRT (Speech Reception Threshold) and SDS (Speech Discrimination Score).

Results: The post-operative audiological results of our patients indicated an average hearing thresholds improvement of 20 dB due to stapedectomy and 51 dB by DACS. Also the SRT (Speech Reception Threshold) improvement was about 40 dB SPL post-operatively.

Conclusion: The post operative results of DACS-implantation show a significant improvement of hearing loss in our patients. This can also be recognized post operatively in comparison with conventional hearing aids. Among the patients, no complications because of the interaction of the two stapes prostheses have been observed until now. There were no changes in bone conduction thresholds pre- and post-operatively. With two patients (50%) recurrent infections occurred around the percutaneous connector. For this reason, future patients in this study will be implanted only with transcutaneous connectors. In principle, the indications of the implantable DACS hearing system also for other mixed hearing loss conditions can be expanded, which will be pursued further after the successful conclusion of the first phase of study.