Cochlear implants

Cochlear Implants and Auditory Brainstem Implants
Cochlear Implants, auditory brainstem implants and their lead systems etc, are regulated as Active Implantable Medical Devices. The MHRA is responsible for ensuring that cochlear implants and auditory brainstem implants placed on the UK market meet appropriate standards of safety, quality and performance, and that they comply with the requirements of the Active Implantable Medical Devices Directive.

Types of hearing loss
There are several types of hearing loss:

• Conductive - caused by problems in the outer or middle ear preventing sound from being conducted properly.  Conductive hearing loss can often be treated by medication or hearing aids.
• Sensorineural - where the sensory cells in the cochlea (the hearing organ) of the inner ear are missing or damaged.  People with profound sensorineural hearing loss who get little or no benefit from hearing aids can often be helped by cochlear implants.
• Neural - where the auditory nerve (which transfers sound signals from the cochlea to the brain) is damaged.  Neural hearing loss can sometimes be treated with auditory brainstem implants

What are cochlear implants and auditory brainstem implants?
Cochlear implants are electronic hearing prostheses that bypass the damaged hearing components by providing electrical stimulation directly to the auditory nerve fibres in the cochlea. The electrical stimulation is interpreted by the brain as sound.

Cochlear implants consist of an external microphone, speech processor and transmitter coil, and an internal stimulator (implanted under the skin just behind the ear) attached to a stimulation electrode which passes into the cochlea.

A variation of the cochlear implant is the auditory brainstem implant where electrodes are implanted directly into the auditory area of the brainstem. This can be used in patients who do not have a functional auditory nerve.

Reporting problems with cochlear implants and auditory brainstem implants
If safety concerns arise with any cochlear implants or auditory brainstem implants, the MHRA will investigate and issue advice to the health service if necessary.

Cochlear implant recipients can report problems directly to us:

• Report an incident

Healthcare professionals who wish to report an adverse incident should note the following relevant guidance:

• General guidance on incident reporting
• Printable poster: Cochlear Implants: Key Reportable Adverse Events (101Kb)
• Report an incident

Infection risks for patients with cochlear implants and auditory brainstem implants
Evidence1,2,3 suggests that patients with cochlear implants may be at an increased risk from pneumococcal meningitis, especially if they have not been immunised against pneumococcal disease.  In August 2002, the Department of Health included cochlear implant patients in the population groups who should be immunised against pneumococcal infection.  Although the risk of contracting bacterial meningitis is low, it is slightly higher than for the general population.  The latest immunisation recommendations can be found in ‘The Green Book’: Immunisation against Infectious Disease: HMSO 20064, which is available online at www.dh.gov.uk (external link).  This recommends that pneumococcal vaccine should be given to all existing and prospective cochlear implant recipients.  This advice is relevant to all patients fitted with a cochlear implant, including those who have previously suffered from pneumococcal meningitis or a pneumococcal infection, and for prospective cochlear implant recipients.

Clinicians implanting cochlear implants and General Practitioners were advised through MHRA communications in 2002 (DA2002(09), 2004 (MDA/2004/046) and 2006 (MDA/2006/019) to determine the pneumococcal immunisation status of their existing and prospective cochlear implant recipients, and to immunise according the Department of Health recommendations.  Ideally, implantation should take place no earlier than two weeks after immunisation has been completed.  However, it is important to note that implantation should not be delayed because immunisation has not been completed.  In these cases, the course should be started at any time prior to or following surgery and completed according to the immunisation schedule.

The Medical Research Council (MRC) Institute of Hearing Research (IHR) published a report1 in August 2004 regarding the increased risk of bacterial meningitis in patients with cochlear implants, following concerns that had been raised in the USA and across Europe.  The IHR report reviewed the situation in the UK and concluded that there is a slightly increased risk of bacterial meningitis for adults who have a cochlear implant, although it is not related to any particular model or type of implant.  The IHR report supports the Department of Health recommendation that cochlear implant recipients are immunised against pneumococcal meningitis.  The full IHR report can be found at www.ihr.mrc.ac.uk/reports (external link).

Larger studies in the USA2,3 have indicated an elevated risk for children compared to adults, and for implants with an intracochlear lead positioner.  The latest of these studies has shown that the risk in children with an intracochlear lead positioner device extends beyond 24 months post implantation.  In the UK, the incidence of infection has not been observed to differ between the available models of cochlear implant.  Implants with a lead positioner are no longer available.

All occurrences of meningitis in cochlear implant patients should be reported to the Medicines and Healthcare products Regulatory Agency following the guidance in the “Reporting problems” section above.

References

1. Cochlear implantation and meningitis in the UK. Report by the MRC Institute of Hearing Research, August 2004, available at www.ihr.mrc.ac.uk/reports (external link).
2. Risk of bacterial meningitis in children with cochlear implants. Reefhuis J et al. N Engl J Med 2003; 349: 435-45.
3. Bacterial meningitis among children with cochlear implants beyond 24 months after implantation. Biernath KR et al. Pediatrics 2006; 117(2):284-9.
4. Immunisation against infectious disease: HMSO 2006; ISBN 0-11-322528-8, with chapter 25 of ‘The Green Book’ (Pneumococcal), available at www.dh.gov.uk (external link).