Tinnitus is a symptom that is highly associated with hearing loss. Its incidence is expected to increase due to the detrimental effects of occupational and leisure noise. Even though no standard treatment is currently available, the effect of cochlear implants on tinnitus in single-sided deafness (SSD) is under scientific attention. This review reveals an overview of all publicly available reports about cochlear implant as a treatment for tinnitus in SSD. Cochlear implantation in SSD suppresses tinnitus in most of the cases. Some studies even demonstrate complete tinnitus suppression after implantation. No tinnitus worsening is reported in any of the cases. Furthermore, tinnitus does not restore during the electrical stimulation presented by the cochlear implant. The tinnitus level seems to stabilize after 3-6 months after the first fitting. Although the underlying mechanism responsible for the observed tinnitus suppression is not yet clear, cochlear implantation should be considered as a treatment option for tinnitus arising from SSD. However, appropriate patient selection is essential as it is expected that it is a requirement that tinnitus arises from cochlear deafferentation.

Earlier studies show that a Cochlear Implant (CI), capable of providing intracochlear electrical stimulation independent of environmental sounds, appears to suppress tinnitus at least for minutes. The current main objective is to compare the long-term suppressive effects of looped (i.e. repeated) electrical stimulation (without environmental sound perception) with the standard stimulation pattern of a CI (with environmental sound perception). This could open new possibilities for the development of a “Tinnitus Implant” (TI), an intracochlear pulse generator for the suppression of tinnitus. Ten patients with single sided deafness suffering from unilateral tinnitus in the deaf ear are fitted with a CI (MED-EL Corporation, Innsbruck, Austria). Stimulation patterns are optimized for each individual patient, after which they are compared using a randomized crossover design, with a follow-up of six months, followed by a 3 month period using the modality of patient’s choice. Results show that tinnitus can be suppressed with intracochlear electrical stimulation independent of environmental sounds, even long term. No significant difference in tinnitus suppression was found between the standard clinical CI and the TI. It can be concluded that coding of environmental sounds is no requirement for tinnitus suppression with intracochlear electrical stimulation. It is therefore plausible that tinnitus suppression by CI is not solely caused by an attention shift from the tinnitus to environmental sounds. Both the standard clinical CI and the experimental TI are potential treatment options for tinnitus. These findings offer perspectives for a successful clinical application of the TI, possibly even in patients with significant residual hearing. TrialRegister.nl NTR3374

Cochlear implantation is a viable treatment option for tinnitus, but the underlying mechanism is yet unclear. Is the tinnitus suppression due to the reversal of the assumed maladaptive neuroplasticity or is it the shift in attention from the tinnitus to environmental sounds and therefore a reduced awareness that reduces tinnitus perception? In this prospective trial, 10 patients with single-sided deafness were fitted with a cochlear implant to investigate the effect of looped intracochlear electrical stimulation (i.e. stimulation that does not encode environmental sounds) on tinnitus, in an effort to find optimal stimulation parameters. Variables under investigation were: amplitude (perceived stimulus loudness), anatomical location inside the cochlea (electrode/electrodes), amplitude modulation, polarity (cathodic/anodic first biphasic stimulation) and stimulation rate. The results suggest that tinnitus can be reduced with looped electrical stimulation, in some cases even with inaudible stimuli. The optimal stimuli for tinnitus suppression appear to be subject specific. However, medium-to-loud stimuli suppress tinnitus significantly better than soft stimuli, which partly can be explained by the masking effect. Although the long-term effects on tinnitus would still have to be investigated and will be described in part II, intracochlear electrical stimulation seems a potential treatment option for tinnitus in this population.

Objectives: Research on tinnitus suppression by intracochlear electrical stimulation has gained interest over the past few decades and it has become easier to apply since the introduction of cochlear implants (CI). This study attempted to gain more insight into optimal stimulation characteristics for tinnitus suppression. Design: Eleven subjects with unilateral CI and tinnitus were recruited from our CI clinic. Electrical stimulation, independent of acoustic sounds, was generated using their CI. The current prospective (single blinded) experimental study systematically assessed two stimulation parameters, namely current level and the anatomical stimulation site inside the cochlea and their short-term effect on tinnitus. Results: Approximately one-third of the tested conditions were successful in which case tinnitus loudness was reduced by at least 30%. At least one successful condition was achieved for nine subjects (82%). Complete suppression was achieved in 6 out of 107 tested conditions (6%). The effect of subthreshold electrical stimulation on tinnitus suppression did not differ significantly from above threshold electrical stimulation. However, a positive relation between mean percentage tinnitus suppression and current level was observed. Pitch-matched electrical stimulation did not appear to suppress tinnitus better than other tested conditions. Conclusions: The majority of the subjects were able to experience tinnitus reduction through intracochlear electrical stimulation independent of acoustic sounds. Tinnitus can be reduced with audible or even inaudible, subthreshold stimuli. Clear trends in optimal stimulation characteristics were not found. Optimal stimulus characteristics for tinnitus reduction therefore appear to be highly subject-specific.

Objective: An often reported side-effect of a cochlear implant (CI) is suppression of tinnitus. However, induction of tinnitus is also a known complication of CI surgery. To date, it remains unclear why some CI recipients experience larger tinnitus complaints due to CI surgery while most others do not. The goal of this study was to investigate the effect of deterioration of residual hearing due to CI surgery on tinnitus. Design: In this retrospective database study, pre- and postoperative audiometric hearing thresholds were retrieved from patients’ clinical files. Furthermore, tinnitus questionnaires were sent to all patients who fitted inclusion criteria. Study sample: Of the 512 CI patients who were implanted within the last ten years, 197 patients fitted the inclusion criteria and returned the questionnaires. Results: We identified 39 cases (19.8%) who suffered from a newly developed (25) or deteriorated (14) tinnitus following CI surgery. No statistically significant association between perioperative deterioration of hearing thresholds measured by pure-tone audiometry and the development or deterioration of tinnitus was found. Conclusions: There is a small risk for deteriorated residual hearing after cochlear implantation. However, for patients with preoperative residual hearing, there appears to be no increased risk of developing chronic tinnitus after hearing deterioration due to cochlear implantation.

Objective: To improve the estimation of the perceived pitch in a single-sided deaf cochlear implant (CI) listener by using accurate 3-dimensional (3D) image analysis of the cochlear electrode positions together with the predicted tonotopical function for humans. Methods: An SSD CI user underwent a Cone-Beam computed tomography (CBCT) scan. Electrode contacts were marked in 3D space in relation to the nearest point on the cochlear lateral wall. Distance to the base of the lateral wall was calculated and plotted against the place-pitch function for humans. An adaptive procedure was used to elicit the perceived pitch of electrically evoked stimulation by matching it with a contralateral acoustic pitch. Results: The electrically evoked pitch percept matched well with the calculated frequency. The median mismatch in octaves was 0.12 for our method in comparison to 0.69 using the conventional Stenvers view. Conclusion: A method of improved image analysis is described that can be used to predict the pitch percept on corresponding cochlear electrode positions. This method shows the potential of 3D imaging in CI fitting optimization.