Cochlear Implants

oPatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.

A cochlear implant is a device that helps improve the hearing abilities of many profoundly or totally deaf people by electrically stimulating the auditory nerve (the nerve of hearing).

In the UK, there are about 700,000 people with severe or profound hearing loss,[1] and more than 45,000 deaf children.[1] (See related separate articles Deafness in adults and Deafness in children).

At present about 10,000 people in the UK have cochlear implants.[2] There are about 20 cochlear implant centres in the UK.[3]

An implant cannot restore hearing to normal but it does give the sensation of sounds. Results vary with each individual - from awareness of environmental sounds to being able to hear speech.[1] Implants work particularly well for adults and children who have lost their hearing after acquiring spoken language and for young children who were born deaf. For someone who has lost hearing, initially the sounds from a cochlear implant are not the same as remembered sounds, but with training they become more natural and meaningful.

With a cochlear implant, environmental sounds can become distinguishable and understanding of speech can improve. The sound that is heard can complement lip-reading. Results vary between individuals, but many patients with a cochlear implant improve their understanding of speech to a useful extent. They may also improve in ability to regulate the volume and pitch of their own voice. Most users of implants find their confidence is improved.[4]

A cochlear implant is an electronic device that stimulates cells of the auditory spiral ganglion to produce a sense of sound. The implant directly stimulates the auditory nerve (the nerve that carries sound from the cochlea to the brain) using electrical signals.

A cochlear implant has two components - external and internal:

  • External component - a microphone and speech processor worn externally behind the ear, and a transmitter coil worn on the side of the head.
  • Internal component - a receiver/stimulator package surgically implanted in the mastoid bone. It receives and translates data into electrical signals that are delivered to electrodes placed in the cochlea.These electrodes stimulate the spiral ganglion cells that innervate the fibres of the auditory nerve. This provides a sensation of hearing.

Various cochlear implant systems exist. For example, there is a totally implantable device available.

General practitioners need to be aware of this technology so that they can refer patients who may benefit from it. If a patient who has had an implant joins the practice list it is important to ascertain that there is support in place from a cochlear implant team.

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Patients and referrals

Referral is to the local ENT consultant who makes an initial assessment and decides whether to refer on to one of the national cochlear implant centres.

The National Institute for Health and Clinical Excellence (NICE) recommends the following categories of patients as being suitable for consideration:[5]

  • Unilateral implants - patients with severe to profound deafness who do not experience adequate benefit from hearing aids after a valid three-month trial (providing that there are no contra-indications and that the hearing aid option is appropriate).
  • Simultaneous bilateral implants - children (infant to 18 years) with severe to profound bilateral deafness or adults who have an additional impairment (eg blindness) that increases their reliance on auditory stimuli as a primary sensory mechanism for spatial awareness.
  • Sequential bilateral implants - these are generally not recommended although those patients who have received a unilateral implant prior to the latest NICE guidance may occasionally be offered a second implant after specialist assessment.

For the purpose of inclusion criteria, severe to profound deafness is defined by NICE as hearing only sounds that are louder than 90 dB hearing loss (roughly: shouting) at frequencies of 2 and 4 kHz without acoustic aids. Specialist tests define the degree of benefit provided by acoustic aids. In addition to the inclusion criteria, there must be no medical contra-indications such as cochlear aplasia or active middle-ear infection.

The team

A successful outcome requires collaboration from patients, families, schools, audiologists, speech and hearing therapists and surgeons. Preoperative expectation shapes postoperative satisfaction and use of the implant. Therefore, all patients and families require counselling from an implant team before such a major undertaking, and a good line of communication is essential

Assessment

Potential candidates will be referred to one of the cochlear implant centres (there are about 20 in the UK) where they receive a multidisciplinary assessment to determine their suitability for cochlear implantation.[5]

The assessment includes:[6]

  • Preliminary tests of hearing and speech recognition - these help to predict outcome. Standard pure-tone and speech audiometry tests are used for screening. A number of speech recognition tests are currently in use, eg the Hearing In Noise Test (HINT), which tests speech recognition in the context of sentences.
  • CT scan or MRI to evaluate the cochleovestibular apparatus and internal auditory canals, eg to exclude cochlear dysplasia. In children or young adults with progressive hearing loss, MRI is required to exclude neurofibromatosis type 2. MRI is better at revealing fluid spaces of the cochlea and is increasingly the primary imaging of choice.
  • The promontory stimulation test is sometimes used:
    • This tests the auditory nerve by stimulating the promontory (in the middle ear) with small pulses. This is carried out under local anaesthetic, and an electrode is inserted through the eardrum. The audiological scientist delivers small amounts of electrical current at different frequencies to the electrode. The patient indicates when they hear a sound.
  • Auditory brainstem response tests may also be used in children.

The operation[6]

The operation is carried out in a specialist centre. It requires general anaesthetic and takes 2-5 hours. The length of inpatient stay is approximately 2-3 days with a further fortnight's rest at home. The processor is only switched on a few weeks after the operation. It will then be 'tuned' by the team to suit the patient. It may take a while to become accustomed to the new sounds.

Postoperative complications

In one study from a UK cochlear implant centre in 2004:[7]

  • Minor complications (which resolved) occurred in 25% of patients.
  • Major complications occurred in 6% and included implant extrusion, implant sepsis, electrode migration, persistent non-auditory stimulation and flap-related problems.

Other potential complications are:[6][8][9]

Hearing rehabilitation[6]

Following cochlear implant there is an ongoing process of rehabilitation (or 'habilitation' for those without previous hearing). This involves, firstly, programming the device - so the user can hear sounds through it and, secondly, the rehabilitation process - learning to 'make sense of' the sounds heard.

The cochlear implant processor is only switched on a few weeks after the operation. It will then be 'tuned' by the team to suit the patient who may take a while (weeks or months) to become accustomed to the new sounds.

Rehabilitation usually involves a team of specialist speech and language therapists, and specialist teachers of the deaf, working at the implant centre and/or in the patient's school or home.

The rehabilitation programme may include a structured set of exercises designed to help the cochlear implant user understand and recognise the sound signal. It might begin with simply detecting sounds, and then move on to distinguishing different sounds, and thence to recognising spoken words.

Generally, once the patient is used to the implant, they can carry on life as usual - but certain sports, equipment or tests should be avoided (see below). The external unit may be replaced as technology progresses. If the internal part fails, this can also be replaced.

DOs and DON'Ts for patients with cochlear implants - and their doctors[10]

Do:

  • Provide pneumococcal immunisation for patients with cochlear implants (to protect against pneumococcal meningitis) - in addition to standard childhood immunisations.[11]
  • Promptly treat ear infection in the implanted ear, with antibiotics. GPs treating such patients should inform the cochlear implant centre promptly. High doses of antibiotics such as amoxicillin or co-amoxiclav, or intravenous antibiotics in some cases, have been suggested.[11]

Don't:

  • Don't use treatments involving electric current or strong magnetic fields to the head or neck. These include: electroconvulsive therapy (ECT), therapeutic diathermy (sometimes known as 'deep heat'), electrical hay fever relievers, neurostimulation, and any device involving electric current to the head and neck, eg TENS machines.
  • MRI scans should usually be avoided - except on the advice of the implant team.
  • Precautions are needed with some devices, eg security scanners, induction cookers.

Further information is available from the British Cochlear Implant Group's safety guidelines.[10]

General points

  • The benefit is highly variable. Overall, studies consistently show statistically significant benefits in various specific areas (such as hearing and speech production) as well as in more general areas (such as quality of life).[5]
  • The age at onset of deafness and duration of deafness before implantation are important.
  • Over 90% of implants survive beyond 11 years.[12]
  • Benefit increases with time and the mode of action appears to be multifactorial.[13]
  • There is evidence that bilateral implants produce a better result than unilateral implants, especially when listening in adverse conditions.[14]

Children

  • Cochlear implants are associated with improvement of hearing, speech perception and speech production.[5] The quality of life as perceived by the child and by the parents has also been noted to improve.
  • Many children with a cochlear implant can develop spoken language. Earlier implantation may lead to better language outcomes.[15] Research suggests that children given a cochlear implant in their first year of age can develop language skills at a comparable rate to normal-hearing children.[16]
  • Sometimes children have multiple handicaps which may not be evident until after implantation. Even if results are less than perfect such children seem to obtain benefit.[17]
  • Bilateral cochlear implants help to improve speech perception in environments such as excessive quiet or noise.[18][16]
  • A multidisciplinary approach is needed both for assessment of the child pre-implant and to maximise the benefit.[5][19]

Adults who are postlingually deaf

  • This term refers to patients who have previously been able to hear and have acquired language.
  • The quality of life in adults given cochlear implants improves, with less isolation and depression.[20]
  • Elderly patients too can benefit from cochlear implants, according to a study of those who are postlingually deaf.[21]
  • One recent study suggests that even patients who are 'borderline' in terms of meeting the criteria for a cochlear implant, may benefit in terms of useful speech hearing and quality of life.[22]
  • Economic benefits: a recent Canadian study found that cochlear implantation was linked to an increase in income and employment rates among recipients, and concluded that there is economic as well as quality of life benefit from cochlear implants.[23]

Prelingually deaf young people and adults[15]

  • This term refers to those who were deaf before acquiring language (eg those born without hearing).
  • Those in this group of patients only rarely develop full spoken language, but many do obtain some benefit from implantation. Therefore age alone should not be an absolute contra-indication to implantation.
  • Any benefit will usually be evident within the first year after the implant.
  • The function of electrodes will probably continue to improve, which may broaden the use of cochlear implants.
  • It is now possible to place a device in the malformed cochlea. When an auditory nerve is absent or when implantation failed despite a functional device, auditory brainstem implants can restore some form of hearing to the deaf.[24]
  • Cochlear implants can be combined with acoustic hearing devices such as electric-acoustic stimulation - this may give greater speech recognition.[25]

Further reading & references

  1. Action on Hearing Loss
  2. Treating hearing impairment, NHS Choices, November 2011
  3. Deafness Research UK
  4. National Cochlear Implant Users Association UK, May 2012
  5. Hearing impairment - cochlear implants; NICE Technology Appraisal Guidance, January 2009
  6. British Cochlear Implant Group
  7. Green KM, Bhatt YM, Saeed SR, et al; Complications following adult cochlear implantation: experience in Manchester. J Laryngol Otol. 2004 Jun;118(6):417-20.
  8. Ovesen T, Johansen LV; Post-operative problems and complications in 313 consecutive cochlear J Laryngol Otol. 2009 May;123(5):492-6. Epub 2008 Oct 10.
  9. Reilly BK et al, Cochlear Implants, Medscape, Jan 2012
  10. Recommended guidelines on safety for cochlear implant users, British Cochlear Implant Group (2010)
  11. Rubin LG; Prevention and treatment of meningitis and acute otitis media in children with Otol Neurotol. 2010 Oct;31(8):1331-3.
  12. Maurer J, Marangos N, Ziegler E; Reliability of cochlear implants. Otolaryngol Head Neck Surg. 2005 May;132(5):746-50.
  13. Yonehara E, Mezzalira R, Porto PR, et al; Can cochlear implants decrease tinnitus? Int Tinnitus J. 2006;12(2):172-4.
  14. Litovsky R, Parkinson A, Arcaroli J, et al; Simultaneous bilateral cochlear implantation in adults: a multicenter clinical study. Ear Hear. 2006 Dec;27(6):714-31.
  15. Peterson NR, Pisoni DB, Miyamoto RT; Cochlear implants and spoken language processing abilities: review and assessment Restor Neurol Neurosci. 2010;28(2):237-50.
  16. Clinical Guidelines for Paediatric Cochlear Implantation. Ear, Nose and Throat Advisory Group, Department of Health, State of Western Australia, May 2011
  17. Wiley S, Jahnke M, Meinzen-Derr J, et al; Perceived qualitative benefits of cochlear implants in children with multi-handicaps. Int J Pediatr Otorhinolaryngol. 2005 Jun;69(6):791-8. Epub 2005 Mar 2.
  18. Sparreboom M, van Schoonhoven J, van Zanten BG, et al; The effectiveness of bilateral cochlear implants for severe-to-profound deafness Otol Neurotol. 2010 Sep;31(7):1062-71.
  19. De Raeve L; Education and rehabilitation of deaf children with cochlear implants: a Cochlear Implants Int. 2010 Jun;11 Suppl 1:7-14.
  20. Mo B, Lindbaek M, Harris S; Cochlear implants and quality of life: a prospective study. Ear Hear. 2005 Apr;26(2):186-94.
  21. Park E, Shipp DB, Chen JM, et al; Postlingually deaf adults of all ages derive equal benefits from unilateral J Am Acad Audiol. 2011 Nov-Dec;22(10):637-43.
  22. Amoodi HA, Mick PT, Shipp DB, et al; Results with cochlear implantation in adults with speech recognition scores Otol Neurotol. 2012 Jan;33(1):6-12.
  23. Monteiro E, Shipp D, Chen J, et al; Cochlear implantation: a personal and societal economic perspective examining the J Otolaryngol Head Neck Surg. 2012 Apr;41 Suppl 1:S43-8.
  24. Deggouj N, Gersdorff M, Garin P, et al; Today's indications for cochlear implantation. B-ENT. 2007;3(1):9-14.
  25. Wilson BS; Partial deafness cochlear implantation (PDCI) and electric-acoustic stimulation Cochlear Implants Int. 2010 Jun;11 Suppl 1:56-66.

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Dr Olivia Scott
Current Version:
Peer Reviewer:
Dr Helen Huins
Document ID:
1974 (v24)
Last Checked:
19/07/2012
Next Review:
18/07/2017