Introduction

As per WHO estimates for India, around 6.3 crore people are suffering from significant auditory loss. The estimated prevalence of adult-onset deafness was found to be 7.6% in the Indian population [1]. Hearing loss has been associated with a variety of disabilities in adults which include depression, social isolation, neurocognitive dysfunction, loss of autonomy, risk of falls, reduced employability, and reduced ability to complete everyday tasks [2,3,4,5,6,7]. Despite these, hearing loss has been considered a stigma of old age. A majority of these will be benefitted from hearing aids who have relatively good speech recognition scores. But for others with poor performance, a cochlear implant (CI) serves as the best option for rehabilitation, especially in patients with bilateral severe to profound hearing loss.

Cochlear implants were first approved for adults in 1985. With increasing experience, there have been wider indications of the cochlear implant procedure. Various technological advancements in the CI make it a safe and effective procedure. In the current era, CI is primarily used for children with prelingual severe to profound hearing loss with good outcomes. We conducted a retrospective cohort study in a tertiary care institute in Northern India to assess clinico-demographical profile and the current aetiologies for hearing loss in the adults undergoing cochlear implantation. We also aimed to evaluate the outcomes of cochlear implantation in such individuals.

Materials and Methods

A retrospective chart review was conducted in the senior author’s unit (RK) of the Department of Otorhinolaryngology and Head-Neck surgery of our institute. The study included adult patients (> 18 years) with bilateral post-lingual severe to profound hearing loss who did not get benefit from the best hearing aid, and who have undergone cochlear implantation from January 2016 to April 2021.

Data were collected from the cochlear implant clinic register regarding demographical and clinical details including age, gender, aetiology, funding of implant, radiological details, pre-operative behavioural and speech audiometry, brainstem auditory evoked response, duration of profound deafness, implant model, surgical details, intraoperative complications, switch-on date, post-operative issues, and post-operative speech audiometry. The duration of profound deafness was calculated from the time at which the patient was previously able to have an interactive telephonic conversation.

All the patients were medically cleared before cochlear implantation. All patients underwent preoperative and post-operative Pure Tone Audiometry (PTA) and speech audiometry in the form of Speech Discrimination Score (SDS) and Speech Reception Threshold (SRT) using standardized Hindi phonetically balanced (PB) words list [8]. All the patients were contacted telephonically to assess the current usage of the cochlear implant and issues. The patients were asked to rate their satisfaction on a scale of 1–10, with 1 representing the least and 10 being the most satisfied. The complications of the surgery were also recorded and divided into major and minor complications. If the complication resulted in a significant medical problem, needed additional surgical intervention, or resulted in permanent disability, it was considered a major complication, else, otherwise.

Descriptive statistics in the form of mean and median were used to describe the data. The pre-operative and post-operative SDS were compared using the chi-square test. A p-value of less than 0.05 was considered statistically significant. Statistical analysis was done using Stata/MP 16 (StataCorp LLC, Texas, USA).

Results

The study included 21 patients with a mean age of 38.6 years (range 18–64 years) with 15 males and 6 females. The aetiology of hearing loss is summarized in Table 1.

Table 1 Aetiology of severe to profound post-lingual hearing loss
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The mean duration of hearing loss before undergoing cochlear implant surgery was 12.7 years (range from 3 to 21 years). Nineteen patients had bilateral profound hearing loss, while two patients had bilateral severe hearing loss with no significant benefit from hearing-aid usage. All patients had a history of usage of a hearing aid in the ear to be implanted. None of the patients could score on tests of open-set speech discrimination.

The implant was government-funded in 9 patients, while 12 patients were self-funded for their implants. The side of surgery was the right ear in all except one patient, who underwent cochlear implantation in the left ear due to the presence of labyrinthitis ossificans in the right ear secondary to chronic otitis media. All patients underwent surgery through the standard posterior tympanotomy approach under general anaesthesia. The model of the implant was Cochlear Nucleus® (Straight no. CI24RE (ST) and speech processor model Nucleus® 5) in all the patients. There was the complete insertion of all electrodes in all the patients, where 14 patients had round window insertion and 7 patients needed cochleostomy. The rate of complications was 1/21 (4.8%), with one patient develo** grade 2 facial palsy. The facial weakness improved over 2 months. There was no issue of device malfunction in any patient. The audiological parameters are detailed in Table 2. In the pre-operative period, SRT was not recordable in any of the patients. The mean post-operative SDS was 74% (range of 50% at 5 months to 90% at 3 months). There was a statistically significant improvement in SDS (p < 0.001). The highest SDS was achieved by a 64-year-old male with progressive hearing loss due to presbycusis, who underwent cochlear implantation 10 years after the onset of profound deafness.

Table 2 Audiological parameters in the pre-operative and post-operative period in patients undergoing cochlear implantation for post-lingual hearing loss
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All the patients are currently using the implant. All patients have reported improvement in speech intelligibility from the day of the last evaluation, except one. The patient has reported that after 1 year of usage of the implant, his speech intelligibility has worsened and he is just able to identify the sounds of a doorbell, ringing phone, and loud noise. The patient could not follow up due to the COVID-19 pandemic. He has been called for an assessment. The median score for the satisfactory outcome of cochlear implantation was 7. The mean duration of follow-up was 44 months (range from 11 to 69 months).

Discussion

The first cochlear implant, Nucleus 22, was approved by the US Food and Drug Administration in 1985 for adults with bilateral profound hearing loss. In the present times, the indications have broadened to include children and adults with less than severe to profound hearing loss. Even after this, CI is widely under-utilized with < 10% of the eligible audiometric candidates being implanted [9, 10]. The reasons are high costs and decreased awareness among the people. The delay in undergoing CI is demonstrated in our study by the finding that adults with profound deafness wait an average of 12 years before being implanted. Although the funding for CI was generated from a governmental organization for 42% of our patients, the majority of the adult patients have to bear the costs from their pocket. With less than 10% of the country’s population having health insurance, the costs are significant to arrange for CI surgery. This aside, several authors have reported on the cost-effectiveness of cochlear implantation on the quality-adjusted life year analysis for patients not benefitting from hearing aids [11, 12].

The major aetiology of hearing loss in our series of adults presenting for CI remains infectious (11/21, 52.4%) with chronic otitis media comprising 42.8% (9/21) of the total cases. Medina et al. conducted a retrospective study in Spain including patients from 2001 to 2015. Otosclerosis was the major cause comprising 28% of the cases which was followed by infectious causes (24%) [13]. In western countries, presbycusis, noise-induced hearing loss, hereditary factors, and ototoxic drug exposure are the common causes of adult-onset hearing loss in patients presenting for CI [14,15,16,17].

We found a significant improvement in speech intelligibility scores of the patients undergoing CI. This is in agreement with the well-established fact in the literature that outcomes of CI in post-lingual deafened adults are good [17]. Although many authors argue that long-term auditory deprivation leads to poor outcomes of CI, our findings suggest otherwise [18,19,20]. We found significant improvement in speech intelligibility of patients who have been implanted as late as 21 years from the onset of profound deafness. In a study comprising 103 adult patients, Medina et al. have shown that the outcomes of CI are not correlated with the long-term auditory deprivation in the implanted ear [13]. The authors suggested that deprivation time may only be a secondary factor in the determination of outcomes in post-lingual deafened adults. Of all patients taken together, the best outcome was reported in our study in a patient with age-induced progressive sensorineural hearing loss.

Cochlear implantation met the expected outcomes for most of the patients and even performed better than the expectation of some as evidenced by a high satisfaction score. The rate of complications of CI in our study was 4.8%, which was a minor complication as this didn’t require any major surgical intervention or change in course of treatment. The overall prevalence of complications was 12.8% as reported in a review by Carlson in 2020 [17]. The prevalence of major complications was 2.7%. The surgery of CI has come a long way to become a low-risk outpatient procedure today.

The implications of the study are limited by its retrospective nature. The sample size in our study is small. This is an indication of a mismatch in the ratio of adults to children presenting for CI. During the same period, the number of paediatric cochlear implantation undertaken in our unit was 148 (unpublished data). We have not evaluated the impact of CI on the quality of life of the patients using standardised methods. We were also not able to evaluate the trend of post-operative speech intelligibility in an individual patient. This is because our patients come from far-off places and prefer to continue speech therapy at their local centres. Hence, they have erratic follow-up schedules.

Conclusion

Cochlear implantation is a safe surgery with good outcomes in post-lingually deafened adults. The major cause for deafness remains infections among those presenting for CI. Adults tend to select the option of CI after a prolonged interval from the onset of hearing loss. There is a need to create awareness among the general population as well as the general physicians regarding the current indications for CI in adults also.