Singapore General Hospital discusses about cochlear implantation uses and how it may be a good alternative for patients to improve hearing outcomes.
Not all patients with sensorineural hearing loss may benefit adequately from hearing aids. In such cases, cochlear implantation may be a good alternative to improve hearing outcomes and boost quality of life for patients both young and old. Learn about its indications, uses and when to refer patients.
WHAT IS SENSORINEURAL HEARING LOSS?
Sensorineural hearing loss (SNHL) is a condition in which hearing loss is due to pathology in the sensory organ of the cochlea, or in the neural pathway between the cochlea and the brain.
Unfortunately, there is no medication or surgery that can repair the damaged inner ear hair cells or the dysfunctional cochlear nerve. Hearing aids are usually prescribed.
LIMITATIONS OF HEARING AIDS
However, as demonstrated in Figure 1, the amplification of sound in SNHL is not straightforward. The more severe the SNHL, the more likely it is to hear significant distortion, and the more likely it is that hearing aids amplify the presenting sound without improving the clarity of the sound.
While someone with severe to profound hearing loss is clearly expected to have reduced clarity, someone with the below audiogram (Figure 2) demonstrating moderate to profound hearing loss may have similarly reduced clarity. This is due to the high-frequency hearing loss interfering with important consonants in the speech banana (superimposed in Figure 2).
While hearing aids do help in many cases of SNHL, some may not derive adequate benefit from them.
With optimised hearing aids, if the patient’s speech discrimination (in a quiet listening environment) is less than 50%, it means they have a less than 50% chance of hearing any given word correctly. Indeed, these patients would struggle even more with background noise.
This usually indicates that the hearing aids do not provide adequate benefit and may indicate that these patients are candidates for cochlear implantation.
WHAT IS COCHLEAR IMPLANTATION?
Cochlear implants consist of two components: an external microphone and a speech processor, which connects transcutaneously via a magnet to the internal receiver stimulator under the skin.
This receiver stimulator converts the sound signals to electrical impulses travelling through an electrode array coiled within the cochlea. These electric impulses stimulate the auditory nerve endings in the modiolus of the cochlea, bypassing damaged hair cells.
THE EVOLUTION OF COCHLEAR IMPLANTATION
Cochlear implants were conceived in the 1950s1 and have come a long way since, from simple singlechannel devices (which still managed to improve the quality of life for patients2 despite not supporting speech understanding), to multi-channel devices in 19843,4.
Current iterations of cochlear implants are slimmer than ever, and have between 12- to 22-channel electrode arrays, with receiver stimulator magnets under the skin that permit MRIs with minimal precautions from 1.5 to 3 Tesla. This is certainly a far cry from 10 years ago when a minor surgery would have been required to remove the magnet prior to an MRI, or MRIs were even completely prohibited.
Cochlear implantation surgery has also evolved to value preservation of remnant cochlear reserves if present (‘soft surgery’), leading to improved patient hearing outcomes especially for music appreciation.
It is an approximately two-hour surgery, and patients can opt to go home the same day or stay one night for observation.
INDICATIONS FOR COCHLEAR IMPLANTATION
All these advancements have led to an expanding range of indications for cochlear implantation.
The primary indication would be having bilateral profound SNHL not improved with hearing aids. However, other valid indications currently are bilateral severe to profound SNHL, or even select cases of moderate to profound SNHL with poor speech discrimination.
USES OF COCHLEAR IMPLANTATION
More recently, more studies have been published demonstrating the efficacy of cochlear implantations in single-sided deafness5 (with one normal hearing ear), or asymmetrical hearing loss (where the contralateral ear also requires a hearing aid).
This is especially crucial in children. Previously, it was thought that with one normal hearing ear, the child develops speech and language normally and hence it was not critical to have binaural hearing. However, studies have shown that whilst some children do cope well, others struggle academically because so much cognitive effort goes into listening in noisy environments and sound localisation6.
In adults, single-sided deafness also affects quality of life7,8 and work performance9. For some, the accompanying tinnitus is worse than the hearing loss. Thankfully, this can be improved with cochlear implantation10-12.
Another impetus for cochlear implantation in singlesided deafness is the possibility of losing hearing in the contralateral ear.
With an ageing population with increased emphasis on quality of life, it is also more common now to see cochlear implantations in the older age group (over 80 years old).
Mr T is a 63-year-old male with a past medical history of hypertension, dyslipidaemia, gout and neovascular macular degeneration.
He had sudden sensorineural hearing loss SNHL in his left ear in 2013 and presented in 2021 with sudden SNHL in his right ear. He had right severe SNHL and left profound SNHL.
Evaluation and work-up
Back in 2013, MRI and blood tests performed did not reveal any abnormalities. Despite treatment, he did not recover usable hearing in his left ear but did not use a hearing aid because he had normal hearing in his right ear.
In 2021, further work-up revealed undiagnosed diabetes, but otherwise the MRI did not reveal causative brain pathology. Unfortunately, there was minimal recovery in his right ear with maximum medical therapy including transtympanic steroid injections. Additionally, he suffered from severe bilateral tinnitus.
Hearing aid use
Mr T purchased a hearing aid which helped a little, but he was still severely disabled and found it extremely frustrating to communicate with family and colleagues.
He was eligible for cochlear implantation bilaterally.
In his left ear, there was a fairly long period of auditory deprivation of eight years (without hearing aid use), which would affect eventual maximum rehabilitation potential.
For the right ear, surgery would have had to be delayed till at least six months after the onset of hearing loss to await spontaneous recovery, but it would have had a much better outcome than implanting the left ear.
In the end, Mr T decided to proceed with left cochlear implantation because he felt that he still had some usable hearing on the right.
One year on, Mr T’s tinnitus is improved when the implant is switched on, and he hears well in quiet environments. He has stopped using the right hearing aid because of perceived lack of benefit.
KEY TAKEAWAYS FOR GPs
As cochlear implant technology improves and implantation become more accessible, it is important that the medical community stays updated so that we can counsel patients on its potential benefits on their quality of life.
Indeed, we should avoid thinking that sensory deprivation and deterioration is an inevitable consequence of growing older.
The next time you have a patient you find yourself shouting at to communicate (or likely just speaking to the accompanying person to avoid the trouble of communicating with a hearing-impaired person), think of whether they would benefit from hearing aids.
If the patient says that they have tried hearing aids but they do not seem to work, they may benefit from cochlear implantation and should be referred on to a specialist.
"The SGH Centre for Hearing and Ear Implants has the largest team of otologists, audiologists and certified auditoryverbal therapists which provides holistic care to our patients with hearing loss and balance disorders. Our team enjoys giving the joy of hearing to all patients, from babies to the elderly.
We have vast experience in hearing implants since our service began more than twenty years ago in 1997. To date, we have performed more than 600 cochlear implants, from ages seven months to 86 years.
We look forward to helping patients be proactive in their hearing health and have clear hearing – an essential ingredient to a happy and socially connected life!"
Dr Vanessa Tan, Director, SGH Centre for Hearing and Ear Implants
Djourno A, Eyries C, Vallancien B. De l’excitation électrique du nerfcochléaire chez l’homme, par induction à distance, a l’aide d’un micro bobinage inclus à demeure [Electric excitation of the cochlear nerve in man by induction at a distance with the aid of micro-coil included in the fixture]. C R Seances Soc Biol Fil. 1957;151(3):423-5. French. PMID: 13479991.
Bilger RC, Black FO, Hopkinson NT, Myers EN. Implanted auditory prosthesis: an evaluation of subjects presently fitted with cochlear implants. Trans Sect Otolaryngol Am Acad Ophthalmol Otolaryngol. 1977 Jul-Aug;84(4 Pt 1):ORL-677-82. PMID: 898520.
Cohen NL, Waltzman SB, Fisher SG. A prospective, randomized study of cochlear implants. The Department of Veterans Affairs Cochlear Implant Study Group. N Engl J Med. 1993 Jan 28;328(4):233-7. doi: 10.1056/NEJM199301283280403. PMID: 8418403.
Gantz BJ, Tyler RS, Knutson JF, Woodworth G, Abbas P, McCabe BF, Hinrichs J, Tye-Murray N, Lansing C, Kuk F, et al. Evaluation of five different cochlear implant designs: audiologic assessment and predictors of performance. Laryngoscope. 1988 Oct;98(10):1100-6. doi: 10.1288/00005537-198810000-00013. PMID: 3172957.
Finke M, Bönitz H, Lyxell B, Illg A. Cochlear implant effectiveness in postlingual single-sided deaf individuals: what’s the point?. Int J Audiol. 2017;56(6):417-423. doi:10.1080/14992027.2017.1296595
Dr Joyce Tang is an Otorhinolaryngology Consultant at Singapore General Hospital with a subspecialty interest in otology and neurotology. She regularly treats patients with hearing loss and did a fellowship with a strong focus on cochlear implants. As a keen musician herself, she is particularly interested in music appreciation for the hearing-impaired.
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