Hearing without ears: do cochlear implants work in children?

Profound deafness in early childhood has major consequences for the child, its family, and society. Critical periods exist for speech and language development during which the developing nervous system is particularly responsive to auditory stimulation. Inadequate sensory input during these periods leads to lifelong linguistic and communicative deficits.¹ Fortunately, if identified early enough, most hearing losses can be satisfactorily managed by hearing aids and rehabilitation. Until the advent of cochlear implantation, however, the outlook for children who were too deaf to hear speech through a hearing aid was less promising and they often failed to develop intelligible spoken language.

Conrad found that the median reading age of profoundly deaf 16 year olds was that of normal hearing 9 year olds and that no fewer than half these children could not read.² As a consequence, their educational and employment opportunities were restricted. In the United Kingdom about 220 children are born each year with hearing losses in excess of 95dB and a further 80 lose their hearing, mainly through bacterial meningitis.³

In profoundly deaf patients auditory nerve fibres remain intact but the sensory neuroepithelium in the cochlea is effectively absent. Thus hearing aids are ineffective as the mechanism in the cochlea by which sound is converted into electrical signals is lost. Cochlear implants overcome this problem by converting sound into electrical signals in a body worn or ear level speech processor. These signals are then transmitted through intact skin to an implanted electronics package that stimulates the auditory nerve endings directly, thus bypassing the sensory end organ.

Cochlear implants are not an alternative to hearing aids. Rather, lack of benefit from an acoustic hearing aid is the essential criterion and generally equates to hearing losses greater than 100 dB. Bacterial meningitis is the commonest cause of acquired severe deafness in early childhood. Meningitis may cause new bone formation in the cochlea, which could technically compromise the insertion of a cochlear implant and such children should be evaluated with some urgency. The vast majority of candidates for implants, however, are congenitally deaf; over 90% of them have normally hearing parents who want their children to hear and speak. Parents who think that deafness is a way of life and not a disability are unlikely to consider implantation. The evaluation process should encompass a child’s social, domestic, psychological, and educational needs. No child should be considered too young or too disabled to be evaluated for cochlear implantation. The delivery of a high quality service for children thus requires well founded multidisciplinary teams, capable of making the complex assessments demanded.

At present about 170 children receive cochlear implants in Britain each year, and the cumulative total of child recipients is over 700. The biological safety of cochlear implantation has been confirmed in a range of laboratory and clinical investigations.⁴ As elective non-use is an option, a major indicator of perceived benefit is continued use of the system. A systematic study of 85 implanted children confirmed use rates approaching 100% three years after implantation.⁵ A longitudinal study comparing speech perception in cochlear implanted children with matched controls who used conventional hearing aids showed significantly better performance in the implanted group.⁶ An uncontrolled longitudinal study of 61 implanted children showed that more than two years of implant use was needed before intelligible speech emerged: an average speech intelligibility score of 40% was achieved after 3.5 years of implant use.⁷ An educational setting that encourages oral rather than signed communication is probably more conducive to developing spoken language skills, but this remains to be confirmed. Emerging evidence suggests that implantation will result in a shift in educational placement in favour of mainstream schooling.⁸ Outcomes from the intervention are variable, but age at implantation seems to be the most important determinant of outcome.⁹ Ideally, a decision to implant should be made before the age of 2—but this demands more efficient neonatal hearing screening programmes than are currently the case.

The cost of generating and maintaining a child user over 10 years approaches £50 000, and it would seem sensible to concentrate this service at fewer centres to maintain expertise and generate economies of scale. No randomised controlled trials have been undertaken on paediatric implantation and would now be impossible to perform given the strength of parental preference and the length of time required to run such a study. However, preliminary estimates of cost effectiveness suggest that the intervention is likely to fall within acceptable limits.¹⁰ Purchasers should recognise that delays in making funding decisions in children can compromise the window of opportunity offered by early implantation. An Audit Commission report was critical of implant providers for giving ambiguous information to purchasers and for variations in price of up to 20% for apparently similar services.¹¹ The recent NHS white papers advocate the establishment of national service frameworks, which should facilitate commissioning and improve equity of access to implantation services.

Today’s children live in a society where prosperity will be determined increasingly by communication skills. Our inability in the past to enable profoundly deaf children the means by which they could communicate competently in the hearing world put these children at an unacceptable disadvantage and incurred an important societal cost. Cochlear implantation has partially broken this barrier and is offering these children unprecedented access to communication skills.