Cochlear implants for adults obtaining marginal benefit from acoustic amplification: a European study

This study aimed to examine the application of a speech recognition score of 30% on open-set word materials as the upper limit for preoperative performance in determining cochlear implant (CI) candidacy for European non-English-speaking hearing-impaired persons. This study also aimed to determine the effect of implantation on residual pure-tone hearing thresholds and to determine the incidence and benefit of a contralateral hearing aid postimplant.

The single-subject design study, involving 20 postlinguistically deafened subjects, compares preoperative performance with hearing aids to postoperative performance with a CI at 6 months after surgery. Subjects were implanted with either the Nucleus Mini 22 or the Nucleus 24 CI systems implementing the MPEAK and SPEAK coding strategies. Fourteen subjects meeting the selection criteria were accrued consecutively specifically for inclusion in the study, whereas the remaining 6 retrospectively implanted subjects were identified for inclusion via patient records.

The investigation included 8 clinics over 3 countries (France, Germany, and Spain) and involved 20 postlinguistically deafened subjects who obtained marginal benefit from acoustic amplification before surgery. Nineteen subjects were older than 18 years of age with 1 subject being 14 years old included in the data report as well.

Open-set speech recognition was evaluated before and after surgery using recorded word lists and sentence lists in the subject's native language to determine benefit from the treatment. Baseline audiograms were obtained before surgery for frequencies of 0.25-8.0 kHz for both ears and compared to pure-tone hearing thresholds measured at 1 month after surgery to determine the effect of the implantation on residual hearing. Additionally, a questionnaire was administered to determine the incidence and benefit of continued hearing aid use in the contralateral ear postimplant.

Nineteen of the 20 study subjects displayed a significant benefit after surgery at 6 months after switch-on for open-set speech recognition. The remaining subject displayed no significant change in performance on objective testing. The implantation resulted in a significant downward shift in hearing thresholds for the implant ear in the majority of subjects. However, 50% of subjects displayed conservation of some residual hearing. For the majority of subjects, hearing aid use in the contralateral ear was discontinued because of lack of perceived benefit after surgery.

The Nucleus Multichannel CI provides a significant benefit for postlinguistically deafened adults who display marginal benefit from acoustic amplification. Therefore, in French-, German-, and Spanish-speaking clinics, a speech recognition score of 30% on open-set word materials is considered an appropriate upper limit for preoperative performance in determining CI candidacy. In view of a significant downward shift in pure-tone thresholds in the implant ear for the majority of subjects, in cases of asymmetry, it is recommended that the poorer ear be implanted. After surgery, the majority of subjects did not perceive an added benefit from continued use of their contralateral hearing aid.