Tinnitus is the perception of sound or noise in the absence of an external physical source. It is a highly prevalent condition and for a high percentage of patients, there is no satisfying treatment modality. For some people, tinnitus has a very severe impact on quality of life, leading to incapacity for work and sometimes even suicidality. The auditory brainstem implant (ABI) is an implant indicated for the restoration of hearing in patients with an hypo-, or aplasia of the cochlear nerve or with dysfunction of the nerve caused by tumor growth in neurofibromatosis type II. It has been shown that the standard intended effect of an ABI has reduction of tinnitus as a welcome side effect in about 66% of the cases. This is in analogy with the promising effect of a cochlear implant (CI) as a treatment for patients with unilateral tinnitus. In this study, the effect of an ABI on severely invalidating, unilateral, intractable tinnitus will be investigated. The ABI may have an advantage over the CI as tinnitus treatment, because CI-implantation leads to destruction of inner ear structures, leading to profound deafness, while an ABI is presumed to not damage anatomical structures. This is the first study to implant an ABI for the primary aim of tinnitus reduction in an intervention pilot study. In total 10 patients with unilateral, intractable tinnitus and severe hearing loss in the ipsilateral ear, will be implanted with the ABI.

Rationale: Tinnitus is the perception of sound or noise in the absence of an external physical source. It is a highly prevalent condition and for a high percentage of patients, there is no satisfying treatment modality. For some people, tinnitus has a very severe impact on quality of life, leading to incapacity for work and sometimes even suicidality. The auditory brainstem implant (ABI) is an implant indicated for the restoration of hearing in patients with an hypo-, or aplasia of the cochlear nerve or with dysfunction of the nerve caused by tumor growth in neurofibromatosis type II. It has been shown that the standard intended effect of an ABI has reduction of tinnitus as a welcome side effect in about 66% of the cases. This is in analogy with the promising effect of a cochlear implant (CI) as a treatment for patients with unilateral tinnitus. In this study, the effect of an ABI on severely invalidating, unilateral, intractable tinnitus will be investigated. The ABI may have an advantage over the CI as tinnitus treatment, because CI-implantation leads to destruction of inner ear structures, leading to profound deafness, while an ABI is presumed to not damage anatomical structures. This is the first study to implant an ABI for the primary aim of tinnitus reduction.

Objective. To evaluate the efficacy of an ABI for the suppression of unilateral, intractable tinnitus and to establish the safety of the ABI for this new indication.

Study design. This is a single center, non-randomized, prospective cohort, intervention pilot study. There is no control group. In this study, 10 patients will be implanted with an ABI.

Study population. Adult patients with invalidating, unilateral, intractable tinnitus and ipsilateral severe hearing loss are included in this study. All study participants have no significant comorbidity and are mentally competent.

Intervention. All study participants receive an ABI, which will be neurosurgically implanted. The ABI will be switched on 6 weeks after implantation. The surgery and post-surgery follow-up and switch-on procedures are consistent with the intended use of the ABI.

Main study parameters. The primary outcome is change in the Tinnitus Functioning Index (TFI). The endpoint is set at 1 year after implantation. Follow up will take place until 5 years after implantation.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness. The implantation, activation and fitting of the ABI will be performed exactly as described in the existing protocols for intended use, however in this study, the ABI is placed for another indication. Implantation of the ABI requires hospital admission for estimated 4 days. After dismissal, patients visit the outpatient clinic at least 8 times in the first year, depending on the amount of fitting session necessary. Implantation of the ABI is an invasive procedure, which potentially can cause severe complications (meningitis 3,8%, transient hydrocephalus 1,3%, cerebellar contusion 1,2%). Other complication that may occur are infection, bleeding, hearing loss and other cranial nerve dysfunctions. By an extensive training program for the neurosurgeon and presence of the experienced surgeon during the first surgical procedures, the investigators feel that neurosurgical risks and risk of device failure due to inadequate implantation can be limited. In this pilot study, the effects on hearing and tinnitus are still uncertain, however based on the results published in literature the investigators are confident that the effects on both will be positive. Nonauditory side-effects and disappointing results on hearing and/or tinnitus can be well managed by altering stimulation strategy or if necessary, by turning off the device. Tinnitus can be severely invalidating with a large impact on quality of life and the ABI is promising in reducing tinnitus in these patients. This study imposes a significant risk on the study participants. However, the investigators feel that the risks outweighs the potential to ameliorate severely debilitating tinnitus.

Inclusion Criteria:

• Unilateral tinnitus
• Severely invalidating tinnitus
• Men or women, age >18yr
• Tinnitus that is present >1 years and was stable during the last year
• Tinnitus that is nonresponsive to indicated conventional existing treatments (hearing aids and cognitive behavioral therapy (CBT)). If a psychologist has indicated that CBT may ameliorate tinnitus complaints, the patient should have tried CBT for long enough time to reasonably argue that these treatments were not successful. This is the same for hearing aids.
• Ipsilateral ear: pure tone audiometry (PTA) thresholds >40dB and <90dB (mean over 1-2-4kHz)
• Functional hearing in the contralateral ear with pure tone audiometry thresholds <35dB (mean over 1-2-4 kHz) and with a minimum Δ25dB compared to the ipsilateral ear.
• Informed consent after extensive oral and written information about the surgery, complications and the uncertain effect of the ABI on tinnitus

Exclusion Criteria:

• Detectable cause for tinnitus that requires causal therapy (e.g. vestibular schwannoma, glomus tumor, otosclerosis, arteriovenous malformation) as investigated by radiological and otological examination
• Psychiatric pathology and/or an unstable psychological situation as declared by a psychiatrist
• Unrealistic expectations as declared by the investigator and/or psychiatrist
• Life expectancy <5 years
• History of blood coagulation pathology
• ASA >II
• Pregnancy
• Anatomic abnormalities that would prevent appropriate placement of the stimulator housing in the bone of the skull
• Anatomical abnormalities or surgical complications that might prevent placement of the Auditory Brainstem Implant Active Electrode Array
• Known intolerance to the materials used in the implant (medical grade silicone, platinum, iridium and parylene C)