Cochlear Implants in Congenitally Deaf Children
CHAPTER 81
The history of cochlear implants is a somewhat recent one. The first experimental single-channel implant was provided to a child in 1980, and the first multichannel implant in a child was completed in Australia in 1985, with multisite trials begun with children in the United States the next year. Since the initial experimental work, it is estimated that about 12,000 to 15,000 persons worldwide have received implants, with approximately one-third of those being children. Most children with implants in the United States, in Australia, and in western Europe are deaf as a result of meningitis (45 to 64%). Those children with implants who are identified as having congenital onset of deafness is still a small subset. The push for early identification of hearing loss, and for early fitting of hearing aids, suggests that our attention will invariably be drawn to that subset of children with profound bilateral hearing loss who do not receive substantial benefit from conventional hearing aids, most of whom will have a congenital onset of deafness. It is readily accepted that any child who acquires deafness after the onset of spoken language and who receives limited benefit from amplification is a potential candidate for a cochlear implant. The analogous situation of an older child, adolescent, or adult who is deafened and is considered for an implant also causes little controversy. The question of an implant for the infant, toddler, or young child who has never had auditory experience should raise many cautions for the physician and implant teams, however.
The cochlear implant is not the end of habilitation in children with congenital deafness. Rather, it is just the beginning, constituting only one factor in the effort to promote the child’s linguistic, educational, psychosocial, and intellectual development. Deafness may be considered a variation in the human condition by some, or a disability by others, but the most critical aspect of the deaf child’s habilitation is the establishment of communication, whether or not an implant is involved. The heavy lifting of language acquisition is accomplished in normal hearing children by the fourth or fifth year of life. In view of the importance of these early years for language acquisition in general, it is an important goal to ensure that the first 4 or 5 years of life are primary language learning years for every child with congenital deafness as well.
The list of controversies surrounding the process of implantation in children with congenital deafness is substantial. The set of controversies discussed in this chapter, although not exhaustive, represents the most publicized and the most vexing issues: (1) advisability of lowering the minimum age for implantation; (2) deciding when benefit from conventional amplification is not sufficient to sustain communication development in a young child; (3) determining whether family and educational resources are sufficient to warrant and support implantation as part of the child’s habilitation, including the question of which modes of communication (spoken versus sign language) seem to be most important to implant success; (4) the issue of deaf culture and how it should enter into parents’ and professionals thinking about implantation; (5) whether or how the perspectives of the child might be taken into account; (6) the advisability of implantation in children with multiple neurologic and cognitive disabilities, including auditory neuropathy; (7) whether published data reflect the full range of outcomes for children who are implanted, to include those children who do not derive benefit or who voluntarily discard the implant; and (8) the implications of animal research on neural plasticity and cortical reorganization in regard to the use of implants in young children with congenital deafness. The best speech-processing schemes remain controversial among manufacturers and auditory researchers. (See comprehensive reports such as the 1997 Acta Otolaryngology supplement or the 1997 American Journal of Otology supplement for detailed information on cochlear implants in children, as well as Parkins1 for further information about processing schemes.)
Minimum and Maximum Age for Implantation and Hearing Aid Benefit
The minimum age for implantation is currently set at 2 years in the United States, with compassionate exemptions granted for children younger than age 2 who are deafened by meningitis, with the threat of cochlear ossification possibly preventing adequate electrode insertion. Data regarding a small sample of early implanted infants (before 2 years of age) show a lack of surgical complications,2 whereas others report improved communication outcomes on children with early implantation.3 The controversy arises when considered with the second issue of how to show hearing aid benefit.
There are both national initiatives and regional efforts to establish universal hearing screening in the United States.4, 5 The stated goal of these initiatives is to identify all infants with early onset of hearing loss by 3 months of age and to accomplish hearing aid fitting by 6 months of age for those infants identified with significant hearing loss. The point of these initiatives is to take advantage of the child’s natural facility for the acquisition of speech and language during the first year(s) of life, a facility that does not depend on exposure to spoken language but that applies across any mode of language expression. If spoken language is the goal, we know that the sooner sensory evidence from the aided auditory channel is incorporated into learning for the child with congenital deafness, the better the outcomes will be. According to this argument, implantation during the first year of life, but certainly before 2 years of age, seems logical. If this approach is taken, however, there is the real risk that insufficient time for hearing aid use, inadequate hearing aid fitting, and inadequate definition of the infant’s residual hearing will mask the child’s aided auditory potential. Infants and toddlers with severe hearing loss who are identified early, and who have the benefits of properly fit hearing aids, as well as family and professional support show clear advantage in the area of communication development.6
Children with severe hearing loss (90 to 100 dB bilaterally) who have the advantage of early intervention outperform children who are congenitally deaf and receive implants, particularly in terms of interpersonal communication development.7 In addition, although accurate and reliable evaluation of hearing sensitivity can be accomplished in infants and toddlers through electrophysiologic and behavioral tests administered by experienced pediatric audiologists, the same cannot be said about the quality of hearing evaluations and habilitation processes everywhere in the United States. Despite the criterion of a minimum of 6 months of hearing aid use before an implant is chosen, children more typically need 1 to 2 years of quality input through a well-fit hearing aid before aided hearing benefits are realized. Implant signal processing is improving, as is hearing aid technology. Because implanted cochleas will be unable to take advantage of present or future hearing aid advances, careful definition of residual hearing, informed fitting of hearing aids, and early intervention that includes appropriate use of amplification must precede any consideration of implantation.
With regard to maximum age for implantation, the data suggest that most children with congenital deafness implanted after age 5, and particularly during or after puberty, will be part-time or nonuser 1 to 2 years postimplant.8, 9
Some data are available regarding adolescents and adults who are congenitally deaf who, after further progression of hearing loss, elect to switch from hearing aid use to a cochlear implant. The individuals in this subset who were long-term dedicated hearing aid users and possessed spoken language before implantation, seem to derive substantial benefit. These persons would likely resemble typical learners in that audition has played a role in their communication development in the first place.10 As suggested, evidence regarding implant outcomes in adolescents and adults who were not hearing aid users and/or who were primarily sign language users suggests far less satisfaction. Implantation in persons in this latter category should be approached very carefully, if it is performed at all.
Family and Educational Support
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