This statement will be published as:
Cochlear Implants in Adults and Children. NIH Consens Statement 1995 May 15-17; 13(2):1-30.For making bibliographic reference to consensus statement no. 100 in the electronic form displayed here, it is recommended that the following format be used:
Cochlear Implants in Adults and Children. NIH Consens Statement Online 1995 May 15-17 [cited year month day]; 13(2):1-30.
Cochlear implants are now firmly established as effective options in the habilitation and rehabilitation of individuals with profound hearing impairment. Worldwide, more than 12,000 people have attained some degree of sound perception with cochlear implants, and the multichannel cochlear implant has become a widely accepted auditory prosthesis for both adults and children. The vast majority of adults who are deaf and have cochlear implants derive substantial benefit from them when they are used in conjunction with speechreading. Many of these individuals are able to understand some speech without speechreading, and some of these individuals are able to communicate by telephone. Benefits have also been observed in children, including those who lost their hearing prelingually; moreover, there is evidence that the benefits derived improve with continued use. New speech-sound processing techniques have improved the effectiveness of cochlear implants, increasing user performance levels to ones previously unseen.
The NIH sponsored a Consensus Development Conference on Cochlear Implants in 1988. Since then, implant technology has been continually improved. Questions unanswered at that time have now been resolved. New issues have emerged that must be addressed.
For example, the performance of some severely to profoundly hearing-impaired adults using hearing aids is poorer than that of even more severely hearing-impaired individuals using cochlear implants with advanced speech- processing strategies. It is possible that cochlear implants could be beneficial for some of these individuals. Therefore, the criteria for implantation should be re-examined. The ability to predict preoperatively the level of performance at which an individual implant recipient will function is highly desirable. Currently, the limited prediction of implant efficacy in a specific individual remains a pressing problem. Agreement does not exist on the definition of a successful implant user. What are the appropriate expectations for individuals using cochlear implants? How is benefit defined and measured? What are the audiological, educational, and psychosocial impacts of this intervention and is it cost-effective? Advancing technology will allow for the modification of existing devices or the development of new devices. It is therefore important to know what risks and benefits are associated with device explantation/reimplantation. Surgical and other risks and possible long-term effects of cochlear implants require evaluation.
Implantation of individuals with multiple disabilities, the elderly, and children, particularly children who are prelingually deaf, engenders special questions. Longitudinal studies are providing information on the development of auditory speech perception and production and language skills in children who are deaf and have a cochlear implant. What educational setting is best for the development of speech and language in these children? Are cochlear implants efficacious in children who are prelingually deaf?
To address these new issues since the 1988 Consensus Development Conference (CDC) on Cochlear Implants, the National Institute on Deafness and Other Communication Disorders, together with the NIH Office of Medical Applications of Research, convened a Consensus Development Conference on Cochlear Implants in Adults and Children, May 15-17, 1995. The conference was cosponsored by the National Institute on Aging, the National Institute of Child Health and Human Development, the National Institute of Neurological Disorders and Stroke, and the Department of Veterans Affairs.
The conference was convened to summarize current knowledge about the range of benefits and limitations of cochlear implantation that have accrued to date. Such knowledge is an important basis for informed choices for individuals and their families whose philosophy of communication is dedicated to spoken discourse. Issues related to the acquisition of sign language were not directly addressed by the panel, because the focus of the conference was to synthesize thoughtfully the new information on cochlear implant technology and its use. The panel acknowledges the value and contributions of bilingual-bicultural approaches to deafness.
This conference brought together specialists in auditory anatomy and physiology, otolaryngology, audiology, aural rehabilitation, education, speech-language pathology, bioengineering, and other related disciplines as well as representatives from the public. After 1-1/2 days of presentations and audience discussion, an independent, non- Federal consensus panel weighed the scientific evidence and developed a draft statement that addressed the following five questions:
Auditory performance, defined as the ability to detect, discriminate, recognize, or identify acoustic signals, including speech, is highly variable among individuals using cochlear implants. Since the 1988 CDC on Cochlear Implants, however, some factors associated with outcome variability are now better understood.
Because of a larger subject sample, the effects of etiology can now be distinguished from other factors such as the duration of deafness and the age of onset. Meningitic deafness does not necessarily limit the benefit of cochlear implantation in the absence of central nervous system complications, cochlear ossification, or cochlear occlusion. Children with congenital deafness and children with prelingually acquired meningitic deafness, for example, achieve similar auditory performance if the cochlear implant is received before age 6 years. In general, etiology does not appear to impact auditory performance in either children or adults.
The age of onset continues to have important implications for cochlear implantation, depending on whether the hearing impairment occurred before (prelingual), during (perilingual), or after (postlingual) learning speech and language. At the time of the last CDC, data on cochlear implantation suggested that children or adults with postlingual onset of deafness had better auditory performance than children or adults with prelingual or perilingual onsets. On average, current data following auditory performance in children over a longer period of time support this finding. However, the difference between children with postlingual and prelingual-perilingual onsets appears to lessen with time. Large individual differences remain within each group.
Previous data suggested that prelingually or perilingually deafened persons who were implanted in adolescence or adulthood did not achieve as good auditory performance as those implanted during childhood, although individual differences were recognized. Current data continue to support the importance of early detection of hearing loss and implantation for maximal auditory performance. However, it is still unclear whether implantation at age 2, for example, ultimately results in better auditory performance than implantation at age 3.
As deafness endures, even in postlingually deafened individuals, some acquired skills and knowledge may decline and some behaviors that work against successful adaptation to a sensory device may develop. Individuals with shorter durations of auditory deprivation tend to achieve better auditory performance from any type of sensory aid, including cochlear implants, than individuals with longer durations of auditory deprivation.
Cochlear implants tend to give people with profound deafness a level of auditory performance that is similar to, or better than, the performance of people with severe hearing impairment who use hearing aids. These data raise the issue of whether cochlear implants might give persons with severe hearing impairment and some residual hearing even better auditory performance than they can attain with a hearing aid. No residual hearing is typically defined as profound hearing loss and no open-set speech recognition. However, the degree of preimplantation residual hearing does not predict postimplantation auditory performance. Research is now addressing the critical distinction between the importance of residual pure tone sensitivity compared with that of overall residual auditory capacities and functional communication status.
Some surviving spiral ganglion cells are necessary for auditory performance with a cochlear implant. Degenerative changes occur in both ganglion cells and central auditory neurons following sensorineural deafening. Although a relationship between the number of surviving ganglion cells and psychophysical performance has been demonstrated in animals, a direct relationship between ganglion cell survival and level of auditory performance in humans has not been shown. Animal studies also suggest that electrical stimulation increases ganglion cell survival and also modifies the functional organization of the central auditory system. The implications of these new findings remain to be determined.
The task of representing speech stimuli as electrical stimuli is central to the design of cochlear implants. Designs vary according to (1) the placement, number, and relationship among the electrodes; (2) the way in which stimulus information is conveyed from an external processor to the electrodes; and (3) how the electrical stimuli are derived from the speech input (and other signals). Changes in cochlear implant design/processing strategies and their effects on auditory performance are discussed in Section 3.
Cochlear implantation has a profound impact on hearing and speech reception in postlingually deafened adults. Most individuals demonstrate significantly enhanced speech-reading capabilities, attaining scores of 90-100 percent correct on everyday sentence materials. Speech recognition afforded by the cochlear implant effectively supplements the information least favorably cued through speech-reading. A majority of those individuals with the latest speech processors for their implants will score above 80-percent correct on high-context sentences without visual cues. Performance on single-word testing in these individuals is notably poorer, although even these scores have been significantly improved with newer speech-processing strategies. Recognition of environmental sounds and even appreciation of music have been repeatedly observed in adult implant recipients. Noisy environments remain a problem for cochlear-implanted adults, significantly detracting from speech-perception abilities. Prelingually deafened adults have generally shown little improvement in speech perception scores after cochlear implantation, but many of these individuals derive satisfaction from hearing environmental sounds and continue to use their implants.
Improvements in the speech perception and speech production of children following cochlear implantation are often reported as primary benefits. Variability across children is substantial. Factors such as age of onset, age of implantation, the nature and intensity of (re)habilitation, and mode of communication contribute to this variability. Using tests commonly applied to children and adults with hearing impairments (e.g., pattern perception, closed-set word identification, and open-set perception), perceptual performance increases on average with each succeeding year post implantation. Shortly after implantation, performance may be broadly comparable to that of some children with hearing aids and over time may improve to match that of children who are highly successful hearing aid users. Children implanted at younger ages are on average more accurate in their production of consonants, vowels, intonation, and rhythm. Speech produced by children with implants is more accurate than speech produced by children with comparable hearing losses using vibro-tactile or hearing aids. One year after implantation, speech intelligibility is twice that typically reported for children with profound hearing impairments and continues to improve. Oral-aural communication training appears to result in substantially greater speech intelligibility than manually based total communication.
The language outcomes in children with cochlear implants have received less attention. Reports involving small numbers of children suggest that implantation in conjunction with education plus habilitation leads to advances in oral language acquisition. The nature and pace of language acquisition may be influenced by the age of onset, age at implantation, nature and intensity of habilitation, and mode of communication.
One current limitation is that children are typically implanted at no earlier than age 2 years, which is beyond what may be critical periods of auditory input for the acquisition of oral language. Benefits are not realized immediately, but rather are manifested over time, with some children continuing to show improvement over several years.
Few studies have used language as an outcome measure. The assessment of speech perception, language production, and language comprehension in young children is particularly challenging. Furthermore, all results in children have been reported for single-channel or feature-based devices only, despite the relatively rapid evolution of alternatives in speech-coding strategies. Oral language development in deaf children, including those with cochlear implants, remains a slow, training-intensive process, and results will typically be delayed in comparison with normally hearing peers.
Although psychological evaluation has previously been a part of the preimplant evaluation process, comparatively little research has been conducted on the long-term psychological and social effects of electing for implantation. Still, the psychological and social impact for adults is generally quite positive, and there appears to be agreement between preimplantation expectations and later benefit. This benefit is expressed as a decline in loneliness, depression and social isolation and an increase in self-esteem, independence, social integration, and vocational prospects.
Many adults report being able to function socially or vocationally in ways comparable to those with moderate hearing loss. Furthermore, they describe a new or renewed curiosity about the experience of hearing and the phenomena of sound. In some cases the experience of implantation becomes an integral part of the individual's identity, leading implant users to participate and share experiences in self-interest and advocacy groups.
Negative psychological and social impact is less frequently observed and is often related to concerns about the maintenance and/or malfunction of the implant and external hardware. Other social insecurities may result from the difficulty of hearing amidst background noise, and from unreasonable expectations of aural-only benefit on the part of the implant user or his/her family and friends.
The assessment of psychological impact in children with implants lags behind that for the adult population, in part because psychological outcome is a factor of audiological benefit, which is realized more slowly in children. Additionally, such assessment must consider the child's family setting. Because language acquisition is closely associated with identity, social development, and social integration, the impact of implantation on a child's development in these areas deserves more study in order to produce useful indicators that can bear upon parental decision-making processes.
Although a cochlear implant can provide dramatic augmentation of the auditory information perceived by deaf children and adults, it is clear that training and educational intervention play a fundamental role in optimizing postimplant benefit. Access to postimplant rehabilitation involving professionals familiar with cochlear implants must be provided to ensure successful outcomes for implant recipients.
Rehabilitation efforts must be tailored to meet individual needs, and protocols should be developed to reflect therapies effective for various types of individuals receiving implants. Therapeutic intervention with prelingually deaf adults may differ significantly in both time and content from that of postlingually deaf recipients.
Pediatric cochlear implantation requires a multidisciplinary team composed of physicians, audiologists, speech-language pathologists, rehabilitation specialists, and educators familiar with cochlear implants. These professionals must work together in a long-term relationship to support the child's auditory and oral development. Although the effects of communication mode in implantation habilitation have not been sufficiently documented, it is clear that the educational programs for children with cochlear implants must include auditory and speech instruction using the auditory information offered by the implant.
The cost-benefit or cost-utility of cochlear implantation must be calculated for children and adults separately. For adults, the cost of cochlear implantation includes the initial costs of assessment, the device, implantation, rehabilitation, system overhead, and maintenance. The benefit or utility is estimated as a function of quality of life over time. On this basis, cochlear implantation whether at age 45 years or 70 years compares quite favorably to many medical procedures now commonly in use (e.g., implantable defibrillator insertion).
Although it appears that the cost-utility estimates for children are also quite favorable, we are still in the early stages of cochlear implant application and cannot yet estimate the cost or potential cost savings that will accrue in the area of (re)habilitation and education.
A cochlear implant works by providing direct electrical stimulation to the auditory nerve, bypassing the usual transducer cells that are absent or nonfunctional in a deaf cochlea. Over the past 10 years, significant improvements have been made in the technology used to accomplish auditory stimulation.
The best performance in speech recognition occurs with intracochlear electrodes that are close to the nerve fibers to be stimulated, thus minimizing undesirable side effects.
Early implants used only a single electrode; it has been found that these single-channel implants rarely provide open-set speech perception. Most recent implants have used multielectrode arrays that provide a number of independent channels of stimulation. Such devices provide more information about the acoustic signal and give better performance on speech recognition. No agreement exists on the optimum number of channels, although at least 4-6 channels seem to be necessary.
Much of the recent progress in implant performance has involved improvements in the speech processors, which convert sound into the electrical stimulus. The best performance comes with speech processors that attempt to preserve the normal frequency code or spectral representation of the cochlea. These are distinguished from feature-based processors, which attempt to analyze certain features known to be important to speech perception and present only those features through the electrodes. A major problem in multichannel implants is channel interaction, in which two electrodes stimulate overlapping populations of nerves. Channel interaction has now been minimized with speech processors that activate the electrodes in a nonsimultaneous or interleaved fashion, which has been shown to improve speech recognition significantly.
A final design issue is the means by which the stimulus information is passed through the skin from the speech processor to the electrodes. In a transcutaneous system, the skin is intact and the coupling is done electromagnetically to an implanted antenna. In a percutaneous system, the leads are passed directly through the skin. The two systems have slightly different surgical complications, which are discussed below. The percutaneous system (1) provides a more flexible connection to the electrodes in case a change in speech processor is desired, (2) is easier to troubleshoot in case of electrode problems, and (3) is magnetic resonance imaging (MRI) compatible. Currently, percutaneous systems are not commercially available.
Magnetic Resonance Imaging (MRI) is increasingly the diagnostic tool of choice for a variety of medical conditions. Implants that use transcutaneous connectors contain an implanted magnet and some ferrous materials that are incompatible with the high magnetic fields of an MRI scanner. Implant manufacturers are redesigning their devices to circumvent this problem. Potential MRI risks should be part of the informed consent procedure for persons considering an implant. The external speech processor cannot be made MRI compatible and should not be taken into the scanner.
Cochlear implantation entails risks common to most surgical procedures, e.g., general anesthetic exposure, as well as unique risks that are influenced by device design, individual anatomy and pathology, and surgical technique. Comparative data of major complications incurred in adult implantation show a halving of the complication rate to approximately 5 percent in 1993. The complication rate in pediatric implantation is less than that currently seen in adults. Overall, the complication rate compares favorably to the 10 percent rate seen with pacemaker/defibrillator implantation.
Major complications, i.e., those requiring revision surgery, include flap problems, device migration or extrusion, and device failure. Facial palsy is also considered a major complication but is distinctly uncommon and rarely permanent. Notably, no mortalities have been attributed to cochlear implantation.
Alterations in surgical technique, especially flap design, have led to a considerable reduction in the flap complication rate, which is particularly relevant to transcutaneous devices. Alterations in surgical technique, particularly in methods used to anchor the device, have contributed to a decrease in device migration/extrusion.
All implants are potentially prone to failure--either because of manufacturing defects or use- related trauma. Pedestal fracture is a problem unique to the percutaneous device, but occurs rarely. Manufacturer redesign has produced electrode arrays that are smaller but sturdier. For the most commonly implanted device, 95 percent of implants are still functioning after 9 years. Most current implants with transcutaneous connectors do not provide self-test capability for the implanted portion, making it cumbersome to test for simple electrode failure, such as open and short circuits. Failure detection is particularly problematic in young children. Device manufacturers should include self-test circuity in future implant designs.
Minor complications are those that resolve without surgical intervention. The most common is unwanted facial nerve stimulation with electrode activation, which is readily rectified by device reprogramming. In percutaneous devices, pedestal infections are uncommon and can be treated successfully with antibiotics, but on rare occasions may require explantation.
Reimplantation is necessary in approximately 5 percent of cases because of improper electrode insertion or migration, device failure, serious flap complication, or loss of manufacturer support. In general, reimplantation in the same ear is usually possible, and thus far individual auditory performance after reimplantation equals or exceeds that seen with the original implant.
Long-term complications of implantation relate to flap breakdown, electrode migration and receiver/stimulator migration. Particularly in the child, the potential consequences of otitis media have been of concern, but as the implanted electrode becomes ensheathed in a fibrous envelope, it appears protected from the consequences of local infection.
Cochlear implants are often highly successful in postlingually deafened adults with severe/profound hearing loss with no speech perception benefit from hearing aids. Previously, individuals receiving marginal benefit from hearing aids were not considered implant candidates. Ironically, such individuals often have less speech perception than more severely deafened persons who receive implants. Recent data show that most marginally successful hearing aid users implanted with a cochlear implant will have improved speech perception performance. It is therefore reasonable to extend cochlear implants to postlingually deafened adult individuals currently obtaining marginal benefit from other amplification systems. Prelingually deafened adults may also be suitable for implantation, although these candidates must be counseled regarding realistic expectations. Existing data indicate that these individuals achieve minimal improvement in speech recognition skills. However, there may be other basic benefits such as improved sound awareness that correlate with psychological satisfaction and safety needs.
Because of the wide variability in speech perception and recognition in persons with similar hearing impairments, all candidates require indepth counseling of the surgery, its risks and benefits, rehabilitation, and alternatives to cochlear implantation. To give adequate informed consent, adult candidates should understand that large variability in individual audiologic performance precludes preoperative prediction of success. Determining implant candidacy requires consideration of both objective audiological variables as well as the subjective needs and wishes of individual candidates. Specific characteristics of potential adult cochlear implant recipients are provided below.
Indications in favor of an implant are a severe-to-profound sensorineural hearing loss bilaterally and open-set sentence recognition scores less than or equal to 30 percent under best aided conditions. Duration of deafness and age of onset have been shown to influence auditory performance with cochlear implants and should be discussed with potential candidates.
In general, when there is no residual hearing in either ear, the ear with better closed-set performance, more sensitive electrical thresholds, shorter period of auditory deprivation, or better radiologic characteristics is implanted. However, when there is residual hearing, the poorer ear should be chosen, provided that there is radiologic evidence of cochlear patency to retain the option for continued hearing aid use and, thus, the potential advantages of binaural sound localization.
Traditionally, implantation candidacy was limited to healthy persons. Although there may be specific medical contraindications to surgery and implantation such as poor anesthetic risk, severe mental retardation, severe psychiatric disorders, and organic brain syndromes, cochlear implantation should be offered to a wider population of individuals. In some circumstances, such as in individuals with low vision, implantation may be a tool to promote independence and other quality-of-life goals.
The medical history, physical examination, and laboratory tests are important tools in candidacy evaluation. Individuals with active ear pathology require treatment and re-evaluation prior to implantation. The standard evaluation includes high-resolution computed tomography (CT) scans that serve to detect mixed fibrous and bony occlusions and anatomical abnormalities. MRI provides better resolution of soft tissue structures and should supplement the CT scan when indicated. These imaging techniques should be used to identify abnormalities that may compromise or impede implant surgery or device use.
The results of electrophysiologic tests do not predict implant success. However, in selected individuals, such as those with cochlear obliteration or in decisions regarding ear of implantation, the results of promontory stimulation may be useful.
Cochlear implants have also been shown to result in successful speech perception in children. Currently, the earliest age of implantation is 24 months, but there are reasons to reassess this age threshold. A younger age of implantation may limit the negative consequences of auditory deprivation and may allow more efficient acquisition of speech and language. Determining whether cochlear implant benefits are greater in children implanted at age 2-3 years as compared to those implanted at age 4-5 years might resolve this issue, but sufficient data are unavailable. It is also not clear that the benefits of implantation before age 2 years would offset potential liabilities associated with the increased difficulty in obtaining reliable and valid characterization of hearing and functional communication status at the younger age. A number of children under age 2 years have received implants, both internationally and in the United States, when it was thought that bone growth associated with meningitis would preclude implantation at a later date. Speech/language data obtained on such children will be helpful in determining the potential benefits of early implantation and therefore may help to guide future policy.
Children age 2 years or older with profound (greater than 90 dBHL) sensorineural hearing loss bilaterally and minimal speech perception under best aided conditions may be considered for cochlear implantation. In the young child, auditory brainstem response, stapedial reflex testing, and/or otoacoustic emission testing may be useful when combined with auditory behavioral responses to determine hearing status. Prior to implantation, a trial period with appropriate amplification combined with intensive auditory training should have been attempted to ensure that maximal benefit has been achieved. When the validity of behavioral test results is compromised by maturational factors, the above criteria should be applied in the most stringent manner (i.e., worse hearing sensitivity, longer trial periods, and so on). Current research may broaden audiometric criteria for candidacy to better reflect functional auditory capacity.
Children should undergo a complete medical evaluation to rule out the presence of active disease, which would be a contraindication to surgery. The child must be otologically stable and free of active middle ear disease prior to cochlear implantation. The radiologic imaging criteria used in adult candidates can be applied to children.
Preoperative assessment should entail evaluation of the child in the context of the home and social and educational milieu to assure that implantation is the proper intervention. In some instances psychosocial factors may be used as exclusionary criteria; however, in most cases it should serve only as baseline data for tracking cochlear implant outcomes.
The parents of a deaf child are responsible for deciding whether to elect cochlear implantation. The informed consent process should be used to empower parents in their decision-making. The parents must understand that cochlear implants do not restore normal hearing and that auditory and speech outcomes are highly variable and unpredictable. They must be informed of the advantages, disadvantages, and risks associated with implantation to establish realistic expectations. Furthermore, the importance of long-term rehabilitation to success with cochlear implants must be stressed. As part of the process of informed consent, parents must be told that alternative approaches to habilitation are available. All children should be included in the informed consent process to the extent they are able, as their active participation is crucial to (re)habilitative success.
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