Cochlear implants and tinnitus treatment
- Many forms of tinnitus are caused by deprivation of sounds, and electrical stimulation has been applied to the promontory for treatment of tinnitus, providing significant relief from tinnitus by supplying input to the auditory nervous system.
- Immediate relief of tinnitus has been reported in approximately 82% of the patients and longer term tinnitus suppression in 45% of such treatment.
- Cochlear implants, therefore, may offer long-term tinnitus suppression in patients with severe sensorineural hearing loss by providing input to the auditory nervous system.
- This chapter provides evidence of tinnitus relief in up to 90% of individuals with severe tinnitus following cochlear implantation.
- An indication for the use of cochlear implants in individuals who are deaf in one ear while having incapacitating tinnitus on that side is provided in this chapter.
- Research in the field of cochlear implants and tinnitus is discussed, and suggestions for future research are made.
- EPS Electrical Promontory Stimulation
- SNHL Sensorineural Hearing Loss
- SSD Single-sided Deafness
- VAS Visual Analogue Scale
Tinnitus is one of the most common otological complaints, affecting 10–15% of the adult population. Various treatments have been developed to suppress or reduce tinnitus. Many forms of tinnitus are now thought to be caused by auditory deprivation, and hearing aids can, therefore, provide relief from tinnitus in some individuals. Reduction of tinnitus following the use of a hearing aid was first reported in 1947 . Later, several studies confirmed the beneficial effect of hearing aids for tinnitus relief. In 1981, a significant improvement of the value of binaural aids compared to monaural hearing aids in reduction of tinnitus and associated problems was reported. The improvement was present in almost half of the individuals surveyed . Similar conclusions were drawn from another study by Surr et al. , in which approximately half of the respondents with tinnitus reported that their hearing aids provided either partial or total relief from tinnitus. Individuals rating their tinnitus as being severe reported partial relief of tinnitus rather than total relief, but other studies showed no effect of hearing aids on tinnitus .
Hearing aids are not useful for treatment of individuals with severe sensorineural hearing loss (SNHL) and tinnitus, but if the auditory nerve is preserved, electrical stimulation of the inner ear can supply necessary auditory input in deaf individuals.
Electrical promontory stimulation (EPS) seems to be a promising tinnitus treatment, providing significant relief. Research on EPS shows at least temporary and partial tinnitus suppression. Immediate relief of tinnitus has been reported in approximately 82% of patients and longer term tinnitus suppression in 45% of these patients . Rubinstein et al.  also described the effect of high-frequency EPS on tinnitus, and the authors advocated that the effect should be investigated with an implantable device. There are indications that cochlear implants may provide long-term tinnitus suppression in individuals with severe sensorineural hearing loss. Cochlear implants have been reported to provide tinnitus relief in up to 90% of patients. There is evidence that deafferentation of the auditory pathway plays an important role in causing tinnitus, and that the effect can be reversed by electrical stimulation of the auditory system via EPS or through cochlear implants. A particularly new indication for cochlear implants is single-sided deafness (SSD) with concomitant incapacitating tinnitus . In this article, results of studies of the use of cochlear implants for treatment of tinnitus are discussed and suggestions for future studies are made.
Electrical Promontory Stimulation and Tinnitus
Nearly 200 years ago, electrical stimulation was first described as possible tinnitus treatment. Only in the 1960s and 1970s, the potential beneficial effect of electrical stimulation on tinnitus was rediscovered. Feldmann  reported suppressed tinnitus by Volta’s platinum–zinc cell. Since then, electrical stimulation as treatment for profound SNHL and tinnitus has been widely investigated. Originally, electrical stimulation of the cochlea was used to assess the integrity of the neural structure in the cochlear prior to cochlea implantation. A side effect of this test in some cases was a suppression of the accompanied tinnitus [9–13].
Electrical stimulation of the cochlea is possible with EPS or round window stimulation. In EPS, a needle electrode is placed on the promontory in order to stimulate the cochlea. This technique has been investigated thoroughly and is used pre-operatively to predict speech reception results with a cochlear implant (CI) [14–16].
Portmann et al.  suggested that the effectiveness of electrical stimulation depends on the electrode placement and electrical stimulation at the round window was better than promontory stimulation. Also, temporary tinnitus suppression was most effective when using positive electrical pulses. In the reported studies, the efficacy of EPS for suppressing tinnitus was done using stimulation for only a very short time in acute experimental set-ups. Repeatability of the tinnitus suppression remains unclear, and the long-term effects of EPS on the cochlea and acoustic thresholds have not been thoroughly investigated .
Cochlear Implant for Bilateral Profound Hearing Loss and Tinnitus
Many people who have bilateral profound sensorineural hearing loss have severe tinnitus. The first report showing that suppression of tinnitus could occur after cochlear implantation was published in 1976 by House . Baguley  and Quaranta  reviewed the results of studies of suppression (or modulation) of tinnitus after cochlear implantation. Recent studies provided additional support of these findings [24, 25].
Picture 2 summarizes the results obtained concerning tinnitus modulation after cochlear implantation [24–32]. It is clear that tinnitus decreased after cochlear implantation in most of the people receiving these implants as treatment. For these individuals, the tinnitus was a secondary complaint to the main problem of deafness.
Cochlear Implant for Single-Sided Deafness and Incapacitating Tinnitus
A small group of people have suffered from SSD, and due to this deafness, incapacitating tinnitus developed. The tinnitus was referred to the deaf ear, with the other ear having normal hearing or showing only moderate hearing loss and no tinnitus. At the Antwerp University Hospital, such individuals received a cochlear implant in the deaf ear in order to reduce tinnitus and also to restore some hearing (Medel Combi 40+ with an M-electrode or Pulsar CI100 with Flexsoft electrode). We studied these individuals in a prospective clinical study to assess the long-term effects of cochlear implantation on tinnitus in people with SSD and ipsilateral incapacitating tinnitus . Twenty-one individuals who received a cochlear implant and suffered from severe incapacitating tinnitus that was unresponsive to other treatments participated in this study. Tinnitus loudness was measured using a Visual Analogue Scale (VAS); loudness perception of tinnitus was recorded with the CI both activated and deactivated. Tinnitus distress was measured using the Tinnitus Questionnaire (TQ) pre- and post-operatively.
All 21 patients reported a subjective benefit when the cochlear implant was activated. Tinnitus loudness was reduced significantly after cochlear implantation.
At the 12-month follow-up exam, the loudness of their tinnitus had decreased from an average of 8.5 to 2.5 on the VAS (of 0–10). Also, the tinnitus questionnaire (TQ) total score decreased significantly. Picture 3 shows the average tinnitus loudness as a function of time.
Cochlear Implantation seems to be a successful treatment of severe tinnitus in patients with SSD. A significant suppression of tinnitus occurred already after 1 month of cochlear implantation. All patients but one had a tinnitus score lower than 5/10 on a VAS. The tinnitus largely recurred when their cochlear implant was deactivated.
The results of this study show that after a long period, tinnitus does not reoccur, and there is no adaptation of the tinnitus to the electrical stimulation presented by the cochlear implants. Long-term results up to 48 months after cochlear implantation also suggest cochlear implantation provides durable tinnitus relief in these individuals (Kleine Punte et al.) . It must, however, be emphasized that other causes of tinnitus have to be excluded before cochlear implantation for tinnitus is recommended and severe depression is a contra-indication.
Experience from the use of cochlear implants to treat patients with tinnitus indicates that electrical stimulation of the auditory nerve can reverse the reorganization associated with peripheral deafferentation that causes tinnitus and thus, reverse plastic changes that may have caused the tinnitus. Also, the increase in activation of the auditory nerve may provide inhibitory influence on the cells in the auditory nervous system, which may play a role in its effect on tinnitus. Enhanced attentiveness to environmental sounds could contribute to the observed suppression of tinnitus. The results from this study suggest that inhibition of tinnitus by cochlear implants is stable, and tinnitus does not return over time. This long-term stability suggests that cochlear implants may permanently suppress tinnitus in these patients. Besides providing significant tinnitus relief, patients with SSD also experienced an improvement in their hearing capabilities after cochlear implantation .
It should be taken into account that other factors may also be responsible for the tinnitus relief obtained after cochlear implantation. Psychological factors may have an influence on tinnitus loudness and tinnitus annoyance: the long inclusion procedure before the implantation includes thorough psychological assistance, which may increase the well-being of the patient. However, in the months before cochlear implantation, no attenuation of tinnitus occurred in our study group, which is consistent with the Blue Mountain follow-up study . Finally, an increased assurance after a recuperation of the auditory function may also have contributed to diminishing the tinnitus annoyance.
Development of Tinnitus After Cochlear Implantation
Although in the majority of cases, cochlear implantation results in an abolishment or suppression of tinnitus, a small percentage of individuals have been reported to develop tinnitus or experience an increase of their tinnitus after cochlear implantation. The reported incidence ranges from 0 to 9% [22, 30, 36–38]. Akdogan et al.  investigated the tinnitus properties due to cochlear implantation and found that 4 out of 17 patients (23.5%) developed tinnitus after cochlear implantation. The mean tinnitus loudness was 17.5 dB SL. Quaranta et al.  reported that 7 out of 41 individuals (17%) developed tinnitus immediately after the insertion of the electrode array for a cochlear implant. However, 1 month later, only two of these individuals still perceived the tinnitus they acquired at the time of the implantation and their tinnitus became mild. Although the risk of getting tinnitus from cochlear implantation is minimal, it is important to counsel candidates about the risk of cochlear implants.
Suppression of Bilateral Tinnitus After Unilateral Cochlear Implantation
A few reports about bilateral tinnitus suppression after unilateral cochlear implantation have been published. A study by Di Nardo et al.  reported complete tinnitus suppression bilaterally in 4 of 9 (44%) individuals who received a cochlear implant in one ear, while four others (44%) experienced bilateral attenuation of tinnitus. Another study performed in 14 individuals who had bilateral tinnitus before implantation reported bilateral suppression of their tinnitus or attenuation of the tinnitus in 12 (86%), while the tinnitus increased bilaterally in 2 (14%) of the participants in the study .
The effect of cochlear implantation on bilateral tinnitus was more extensively described in a study performed in 41 individuals with bilateral tinnitus . When their cochlear implant was turned on, the tinnitus was abolished bilaterally in 23 participants of the study (56.1%). Tinnitus was completely suppressed in the implanted ear only in 4 (9.7%) individuals and contralaterally in 4 (9.7%) of the participants. That means tinnitus suppression occurred in 31 (76.5%) participants in this study. Patients with bilateral tinnitus sometimes experience tinnitus suppression after sequential bilateral cochlear implantation . Increase of tinnitus was also described after bilateral cochlear implantation, similar to tinnitus aggravation after unilateral cochlear implantation.
Although many reports of tinnitus suppression after cochlear implantation have been published, more detailed studies are needed to assess the advantages of cochlear implants for treatment of tinnitus. Since double- blind studies are impossible in the field of cochlear implantation, the emphasis should lie on conducting randomized controlled studies on the effects of cochlear implantation on tinnitus. Also, the working mechanisms of tinnitus suppression after cochlear implantation are not totally understood and need to be further explored in studies of humans.
Tinnitus can be influenced by electrical stimulation of the inner ear, at least when the tinnitus occurs in connection with sensorineural hearing loss. Transtympanic electrical promontory stimulation or round window stimulation can provide temporary tinnitus relief. In individuals with profound hearing loss, cochlear implantation can provide more permanent tinnitus suppression.
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