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Special Issue: Emerging trends in cochlear implant

Evaluating cochlear implant candidacy

Recent developments

Dowell, Richard C.

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doi: 10.1097/01.HJ.0000286402.57307.ed
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Cochlear implantation has been proven a safe and effective means of restoring auditory skills in people with severe, profound, and total hearing losses. Modern implant systems are generally similar in design, consisting of an intracochlear electrode array, implanted electronics, and an external signal processor. Although signal processing parameters vary across manufacturers, the major cochlear implant (CI) systems all present a representation of the spectrum of acoustic signals along the electrode array following the assumed tonotopic arrangement within the cochlea.

Electrical current is controlled to represent amplitude changes within frequency regions. Electrical stimulation pulse rates vary from 250 to 4000 Hz, or higher, per electrode. Although higher presentation rates imply increased temporal resolution for the signal delivered to the cochlea, the effect on speech perception has been neither consistent nor predictable.

This paper will summarize the issues facing prospective CI recipients and their audiologists in deciding whether or not to proceed. It will highlight the process involved rather than prescribe exactly who is or is not a CI candidate. Given all the information available about the auditory skills of CI users, I will argue that a scientific evidence-based approach can be followed in most cases. It is also well accepted among experienced practitioners that potential CI recipients and their families should have the chance to make an informed decision based on the best possible information.

WHAT ARE WE TRYING TO ACHIEVE?

The answer to this question is not as obvious as it may seem. The simplest description of cochlear implantation is the replacement or restoration of auditory skills that have been lost due to inner ear pathology. But the ultimate goal or desired benefit from implantation may be quite different for children and adults, for those with pre-lingual and post-lingual hearing loss, and for patients and professionals. The cochlear implant is almost always a means to an end, not the end itself. The end usually is related to improvement in communication and the resulting benefits.

So, in evaluating a patient we must first ask, will a cochlear implant improve this person's auditory skills? And, if so, how will the improvement benefit communication? An additional step is to ask if the predicted communication benefit is in line with the patient's goals, needs, and expectations, but this is more about the informed consent process than the actual evaluation.

In general, improved auditory skills for post-lingually deaf patients do enhance speech perception, and the major benefit of implantation is improved conversational skills in a variety of conditions.

For the families of young, pre-lingually deaf children, the perceived goal is often the development of spoken language.1 This is further removed from the direct effect of the cochlear implant, i.e., the improvement of auditory skills. Adequate auditory perceptual skills may be necessary for the development of speech, but they are not sufficient. Language development, cognitive skills, neural plasticity, and the level of exposure to meaningful auditory input are implicated strongly in the level of speech production proficiency for a hearing-impaired child.1 Understanding that the CI is an auditory device and that communication benefits will depend on additional factors is crucial to the informed consent process for candidates and their families.

So, in the context of providing recommendations about cochlear implantation, we need to ask if it is likely to improve the patient's auditory perceptual skills. An affirmative answer means the patient is a candidate for the procedure. We must then advise patients and their families about the realistic potential for these improved auditory skills to improve communication. This information should help them decide whether or not to proceed.

KEY CLINICAL QUESTIONS

Cochlear implantation cannot be equated with conventional amplification, as there are risks associated with the surgery, the costs are much higher, and a greater commitment of time and effort is required of implant patients than of persons who acquire hearing aids. Therefore, it is important to establish that there is a strong probability of significant improvement in auditory skills if a patient receives a cochlear implant.

Historically, implants were first applied to adults with nearly total bilateral hearing loss, so almost any level of useful auditory skill could be considered a bonus.2 However, as outcomes have improved and implantation become more routine, many candidates today have significant residual hearing. Therefore, evaluating potential benefits has become more complex.3 However, the key question remains the same: Based on current research, experience, and individual evaluation, does a particular candidate have a good chance (let us suggest >75%) of improved auditory skills if he or she proceeds with cochlear implant surgery?

If we can determine this, only one other key question remains: Can the implant device be placed safely into the cochlea and will it have the potential to generate an auditory percept?

Pathologies affecting the structure of the inner ear may make surgery difficult or impossible. Middle ear pathologies create an unacceptable infection risk. Health problems of various types increase the risks of anesthesia. A cochlear implant may be an inappropriate treatment for pathologies that affect the central auditory nervous system or the auditory nerve directly.

Audiologists and surgeons must work together closely to address these issues. The audiologic evaluations, particularly in terms of choice of procedures and their interpretation, can be important in helping the surgeon make the right clinical decision.

The two questions I have posed may seem simple, but to provide answers with the desired level of confidence may be extremely difficult. I will now outline some techniques useful in helping clinicians and patients through this process and will discuss recent developments that have broadened the application of implants.

Prospective cochlear implant recipients fall, reasonably naturally, into three groups with significantly different pre-operative considerations. These are: adults with acquired hearing loss, adults with pre-lingual onset hearing loss, and children.

ADULTS WITH ACQUIRED HEARING LOSS

This group provides the best opportunity for making evidence-based recommendations. There are abundant data on this group in terms of post-implant auditory skills, particularly for speech-perception outcomes. These data can be used to formulate criteria for implantation based on pre-operative assessments with conventional amplification.

Predictive factors

Numerous studies have identified significant predictive factors for speech-perception results in CI users. Several studies identify duration of profound hearing loss as having a significant negative correlation with speech-perception outcomes.4–6 It is sometimes unclear in these studies whether this duration of deafness refers to the implanted ear or to bilateral profound deafness. On the other hand, it appears that both parameters may significantly affect outcomes.

Overall duration of bilateral profound deafness may give a crude indication of the potential loss of central auditory processing skills, which in turn may limit a patient's ability to learn to process the novel signal from a cochlear implant. The duration of deafness in the implanted ear (which may differ from bilateral duration) is expected to correlate with the level of deterioration of ganglion cells in the cochlea, another factor that could limit perceptual performance.

Mixed results are observed in the literature when the age at implantation is considered as a factor.7,8 Some studies have shown no significant effect, others suggest a slight decline in performance with age. Studies that grouped adult patients based on etiology have generally failed to show significant effects.9,10 The duration of implant use has been shown to affect speech-perception results, which raises the issue of when to assess implant users to be sure their performance has reached a plateau.

Generally, speech perception improves rapidly over the first 3 months of implant use, with limited changes occurring later.11 On the other hand, some percentage of implant recipients appear to take a year or more to reach a plateau in their auditory skills. Mostly because of practical constraints on follow-up, it has become the convention in CI work to assess adults approximately 3 months post-implant, on the assumption that most patients have reached their optimum performance at this stage. Because of the availability of 3-month data on many recipients, clinical practice tends to be guided by performance at this point in time.

Blamey et al. performed perhaps the most comprehensive analysis of speech-perception outcomes for adults with acquired deafness by collecting information on 808 subjects from centers around the world.12 This study showed significant effects for duration of deafness, age at implantation, and duration of device use, and some minor effects for particular etiologies.

However, since this study was conducted, the composition of the adult population receiving CIs has changed dramatically. In particular, many more recent implant recipients have useful residual hearing and continue to wear a hearing aid in the opposite ear. This introduces new variables, including the level of pre-implant speech perception, that make estimating “duration of deafness” problematic.

How much hearing is too much?

Summerfield and colleagues have used data from a large cohort of adults with acquired deafness on open-set sentence tests to construct a function relating speech-perception performance to the duration of profound hearing loss in the implanted ear.13 By comparing the speech perception of hearing aid users with the distribution of results for implanted subjects, the clinician can estimate the odds of improved performance. This provides evidence to use in deciding whether or not to recommend a CI. Reviewing the duration of deafness and perceptual performance for each ear separately may help the clinician decide which ear may be more suitable for implantation.

Dowell and colleagues have also used the distribution of results for implanted subjects to develop evidence-based criteria to guide recommendations.3 In this study, speech-perception outcomes for a large group of adult CI users were reviewed. In this population, more than 50% used hearing aids prior to implantation and had significant speech perception in at least one ear. This reflects an overall difference in the population of adults receiving implants in Australia compared with the U.K.

Three groups of implantees were identified with significantly different speech-perception outcomes. Those with a pre-lingual onset of hearing loss performed worse than those with a clearly post-lingual onset. Those with significant residual hearing and speech perception before implantation performed significantly better than others with post-lingual hearing loss.

These results suggest that these groups should be treated separately when it comes to advising them about potential benefits from CIs. Patients with poor pre-implant auditory skills can be treated in the “traditional” way in which the potential for benefit from an implant is fairly clear, but the degree of benefit may depend on the duration of profound deafness, age, and other factors.

Patients who are still using hearing aids effectively need more careful attention. It is essential that their amplification be optimized by means of accepted prescriptive fitting methods. Then the clinician must assess each ear separately and the binaural condition using speech-perception tests to determine the level of benefit from conventional amplification, the differences in performance for the two ears, and the level of binaural advantage. Only then is an evidence-based recommendation possible.

From the distribution of post-implant results, Dowell and colleagues showed that 75% of implant users scored above 70% for open-set sentence testing at their 3-month post-operative evaluation (see Figure 1).3 Based on this observation, candidates whose best scores fell below 70% had at least a 75% chance of improvement with an implant. Similar criteria were developed for other tests of speech perception, including monosyllabic word tests and sentence perception in competing noise. But what about those who do not improve?

Figure 1
Figure 1:
The distribution of open-set, sentence-perception scores for a group of adult CI recipients with useful pre-implant residual hearing. Adults considering implantation who score less than the first-quartile score (70%) have at least a 75% chance of improvement with a cochlear implant.

Considering the down side

The previous discussion showed a method for using known outcomes to predict the potential benefit for implant candidates. However, an informed consent process must also consider what happens when things go wrong. A 75% chance of improvement implies a 25% chance that performance will decline. For instance, if the ear being considered for implantation scores 70% for open-set sentences with conventional amplification, this natural hearing is likely to be destroyed by the implant surgery. If the CI provides unexpectedly poor results, the candidate may be dissatisfied.

Fortunately, there are usually two ears to consider and their speech-perception performance often differs considerably. So, it would appear that a criterion is needed for the implanted ear in addition to the criterion for comparing best-aided performance.

What level of speech-perception performance in the ear to be implanted provides minimal risk of decreased performance? Again, we can refer to the post-implant results showing that a score of 40% or better for open-set sentences is achieved by 95% of implant users in the residual hearing category. So, if the ear to be implanted scores below 40% (and corresponding criteria can be determined for other tests), the chance of decreased performance with a CI is less than 5%.

These arguments have formed the basis of the approach followed in Melbourne over the last 5 years for assessing post-lingual adults considering implantation. When best-aided performance with optimized conventional amplification is worse than 70% for open-set sentences (and/or corresponding criteria for other tests) and performance for the ear to be implanted is below 40%, then candidates can be informed with confidence that there is a 75% chance of improved overall performance and less than 5% chance of decreased performance. In the worst case, there is the potential loss of the binaural advantage and the possible reduction of speech perception on the implanted side from 40% to 0%. Note that this approach always designates the worse ear (for speech perception) as the ear to be implanted in this group of candidates.

The Melbourne clinic applied these criteria from 1999 to 2002 with 45 adult subjects receiving implants under the modified guidelines. By definition, these subjects had sentence perception scores between 40% and 70% in their best-aided condition and one ear with a score below 40%. All subjects were implanted in the poorer ear.

Of the 45 patients, 36 (80%) showed improved speech perception with their CI over their best-aided performance pre-implant. All but one patient (98%) showed improved speech perception with their implant compared with the pre-implanted performance in that ear. These results agree closely with the expected outcomes based on considerations of the distribution of results, and they provide good evidence for the validity of this approach.3

Audiometric interpretation

The starting point for almost all evaluations of the auditory system is the pure-tone audiogram. Although recommendations about cochlear implantation should always be based around speech-perception results, the audiogram and aided thresholds can provide additional useful information. Flynn and colleagues have demonstrated that adults with sensorineural hearing losses in the severe and severe to profound range show a wide range of speech-perception abilities.14 In this group, there were individuals with a pure-tone average hearing loss close to 60 dB HL who scored well below 30% for open-set sentences and would probably benefit from a cochlear implant. Others had four-frequency pure-tone averages (PTAs) close to 100 dB HL, yet scored above 90% for sentence perception.

We must be aware of these possibilities and not judge a patient's candidacy simply on the audiogram. However, there is a significant relationship between degree of hearing loss and speech perception, and it is worth investigating this in interpreting the audiometric information. Flynn's study and additional information obtained in the pre-implant assessment of implant candidates show the relationships between average hearing loss and sentence perception in quiet and in 10-dB SNR competing noise (Figure 2).

Figure 2
Figure 2:
Linear regression relationships between sentence-perception scores and hearing loss for adult hearing aid users. The dotted line shows the best-fit linear function for sentence perception in quiet. The solid line shows the corresponding function for sentences in +10 dB SNR competing noise (data from Flynn14). Mean scores on the same speech-perception tests for adult CI recipients are plotted on the same axes. The data suggest that CI recipients have speech-perception ability similar to that of hearing aid users with losses in the range of 65 to 80 dB HL.

The mean results for CI recipients are plotted onto these regression lines and show a similar mean and range to hearing aid users with four-frequency PTAs between 66 and 77 dB HL. One would certainly not decide whether or not to recommend a CI on the audiometric information alone, but these results do provide a guide to which subjects should be considered for further evaluation and they help identify those who are better off with conventional amplification.

This type of information makes it reasonable to conclude that cochlear implants may be beneficial for any patient whose bilateral four-frequency PTA hearing loss exceeds 80 dB HL. When hearing is better than this rather arbitrary cut-off, there may be isolated cases where a CI would be considered, but only where speech perception is much worse than expected based on the audiogram (possibly involving forms of auditory neuropathy/dys-synchrony).

Aided thresholds

The aided thresholds can also provide useful information for the pre-implant evaluation, but there are many provisos. A concerted effort is required to establish that the hearing aids being used are appropriate for the hearing loss and that they have been programmed and adjusted according to accepted prescriptive guidelines.

Assuming that the aided thresholds are optimized, a useful comparison is to review the patient's ability to access speech information in the mid- and higher frequencies (1000 to 4000 Hz). It is well established that, with appropriate programming, CIs provide good access to speech sounds across this range. This comparison can then add to other evaluations for the purpose of predicting the benefits of proceeding with a CI.

MEDICAL/SURGICAL ISSUES

We now cross over into medical and surgical issues that may affect implantation. I will not go into detail on these issues, but I will summarize some key areas where audiologists need some understanding and often play an important role.

Etiology of hearing loss

Determining the cause of hearing loss is not often straightforward, but some pathologies, such as chronic middle ear disease, cochlear otosclerosis, Ménière's syndrome, and head injury, provide relatively clear evidence. Many other cases (often >50% of post-lingual adults) fit the “unknown progressive” mold. As understanding increases of genetic abnormalities that affect the multiple proteins required for normal cochlea function, we are getting better at understanding and identifying these pathologies. There are audiologic and medical considerations for many of the known etiologies.

Active middle ear disease is a contraindication for implant surgery, as it raises an unacceptable risk of post-operative infection or labyrinthitis. Audiologists need to assist surgeons in monitoring middle ear status as they attempt to bring the condition under control. This may require surgery and up to 6 months of “settling down” before the implant surgery proceeds.

Cochlear otosclerosis often involves the demineralization of bone of the otic capsule. This can be observed on modern imaging (CT scan, MRI) and may compromise the placement of the electrode array or make it less ideal. In addition, these patients face an increased risk that electrical stimulation will affect the facial nerve at some positions. This rarely affects overall auditory performance, but it is a consideration in the informed consent process.

Retrocochlear pathologies are difficult to identify in patients presenting for cochlear implantation. Audiologic assessments aimed at identifying these pathologies rely on some residual hearing. Imaging will detect any CPA tumors, and the surgery for removal may compromise the use of a cochlear implant for that ear. Other, more unusual forms of retrocochlear pathology may include generalized effects on the auditory cortex and brainstem due to trauma, previous surgery, radiotherapy, or disease (meningitis or encephalitis). These cases require individual care and attention from the clinical team. In some cases, electrical stimulation of the promontory test may help establish if there may be benefit from an implant.

Older patients

From the start, there has been much discussion of the effect of age on potential risks and benefits of cochlear implantation, and of whether or not age should be a criterion for implantation. From the early 1980s until today, the suggested age criterion has risen from 65 to 75 to 85 years, and it now appears there is effectively no set age limit.

Why should there be an age limit? Three factors may be relevant here.

  1. We have evidence that older CI patients have somewhat poorer speech-perception outcomes.4,7,12
  2. Older patients are more likely to have health problems that could increase the risk of surgery.
  3. From the health economics perspective, providing expensive technology to younger patients has a greater health utility gain because they are likely to survive longer.

A recent study of outcomes for older patients revealed only minimal differences between implant users over 70 and younger patients.15 Indeed, there is evidence that any differences seen in the immediate post-operative period may lessen over time. Thus, there is very little support for the idea that older patients should not receive a cochlear implant because they do not do as well.

The health risks are, however, challenging for many older candidates. For an elective procedure, the risk of major medical complications needs to be as small as possible. Despite the potential quality-of-life benefits that many older patients may enjoy if implanted, surgeons and anesthesiologists must carefully consider the likelihood and consequences of complications in this group.

Vestibular considerations

Recent studies have quantified the effect of CI surgery on residual vestibular function in the implanted ear.16 In patients who have vestibular function in the implanted ear, there is a significant chance of balance disturbance after surgery. Some patients report balance disturbance in the immediate post-operative period and this correlates with differences in objective measures of vestibular function between pre- and post-surgery. In most cases, the balance symptoms resolve over a period of weeks, but the problem is sometimes more long-term.

Although objective measures suggest that changes in vestibular function are similar for younger and older patients, a disproportionate number of older patients have ongoing problems. This is consistent with reduced neural plasticity in the older group leading to slower compensation. The situation is exacerbated by the fact that older patients are more at risk of falls due to deteriorating vision, reduced muscle strength, and peripheral neuropathies. It is suggested that for older CI patients due consideration be given to the possibility of balance disturbance and the management of the problem if it arises.

Psychological considerations

Adults with hearing loss are more susceptible to psychological and psychiatric disturbance than the general population. The decision to undergo CI surgery and the actual procedure are undoubtedly traumatic. Superimposed on the anxiety of a medical procedure are the hopes and expectations that the implant will “change my life” and the disappointment that first-time recipients often feel when they initially use their speech processor.

Audiologists and others who deal with patients should take an empathetic approach to these situations and be able to recognize when there is evidence of genuine psychiatric disturbance. Ideally, a CI team would benefit greatly from a psychologist with experience in hearing loss and easy access to psychiatric referral.

Exaggeration of hearing loss

Because of the extensive publicity given to cochlear implants, it is not unusual for hearing-impaired adults to gain the impression that a “bionic ear” will be better than their current hearing aids, whatever their degree of hearing loss. Prospective patients are sometimes aware of the type of hearing loss and level of speech perception that would bring them into consideration for implantation. In such cases, they may exaggerate their pure-tone thresholds and perform poorly on speech-perception testing.

This is not as rare as one might imagine, and some of these patients may not be detected as the clinicians are focused on preparing them for the CI. Therefore, audiologists should look for any inconsistencies among reported communication difficulty, observed communication difficulty, and measured speech-perception performance. Objective measures such as acoustic reflex testing, otoacoustic emissions, and, if necessary, evoked potential testing (ABR, cortical responses) can sort out most of these problems.

There are also the truly unusual cases of people with normal hearing attempting to obtain a cochlear implant. Again, if the quality of the audiology is good, these situations will be detected. But there are undoubtedly some CI recipients out there who should never have been implanted.

ADULTS WITH PRE-LINGUAL ONSET HEARING LOSS

As described by Dowell et al,3 adults with pre-lingual onset of bilateral hearing loss perform more poorly than those with acquired deafness. Apart from this overall difference in expectations, similar evaluation techniques can be applied to this group as described earlier. We can use the distribution of outcomes within this group to compare with individual speech-perception scores obtained with optimized conventional amplification to estimate the probability of improvement.

Studies of older children and teenagers with CIs suggest additional factors that can provide guidance on speech-perception outcomes.17 Language development, as assessed by a receptive vocabulary test, duration of profound hearing loss, and pre-operative speech-perception performance were significant predictive factors for speech-perception outcomes.

The work of Blamey and colleagues has firmly established the link between language development and the potential for speech perception with a cochlear implant (or hearing aid).18 Their comprehensive study of 87 hearing-impaired children showed that language development was a far stronger predictor of speech-perception ability than any other parameter addressed in the study, including degree of hearing loss or age at fitting or implantation.

Pre-operative speech-perception ability for congenitally deaf adults and older children is an indicator of their ability to process auditory information for speech perception. If they score significantly on an open-set speech test using their limited hearing, it is a positive indicator that they will be able to use CI input successfully. If their speech perception is poor, despite useful residual hearing, they may have difficulty processing the implant signal.

In summary, evidence-based recommendations are possible for pre-lingually deaf adults based on the distribution of implant outcomes for this group and knowledge of their hearing history, language development, and use of residual hearing.

CHILDREN

In children, the benefits of implantation for speech perception and development of language and speech production are well established.1,19 Many studies, although not all, indicate that earlier implantation improves the prospects of high-level outcomes. Thus, we see a strong trend toward implanting children as young as possible. In the future, pediatric CI programs will deal mostly with children 2 years and younger, and the advent of neonatal hearing screening will advance evaluation into the first few months of life.

Assessing speech perception to decide if a child should be implanted will usually be impossible as most children will be in the early stages of language and cognitive development. For these patients, we need to ask, is the potential to develop auditory skills with a CI significantly better than the potential with conventional amplification? This is difficult to know in very young children. We can, however, use our experience with adults and older children to guide these decisions.

For children as young as 7–8 months, it should be possible to use established pediatric techniques to determine behavioral audiometric thresholds and optimum aided thresholds. The reliability of the audiometric information is important, as it will largely guide decisions about implantation. We now have a battery of objective hearing tests that can estimate hearing levels at any age. These include the transient-evoked ABR, otoacoustic emissions, and auditory steady state responses (ASSR).

Although these assessments provide valuable information, there is always a possibility of error and inconsistency. One inconsistency that used to puzzle audiologists is the finding of auditory neuropathy (AN), in which neural responses appear to be absent but there is evidence of cochlear function. AN is now a recognized condition and CIs have been used with people diagnosed with it. However, this is only one possible pattern of results that could indicate that something is awry (this may be as simple as a poorly calibrated evoked response device).

It is still difficult to recommend implantation without both behavioral and objective evidence showing a consistent level of hearing loss.

Earlier, I presented data on the relationship between hearing loss and speech perception in adults and mapped the average results for CI patients onto this function to provide a guide to the levels of hearing loss that may benefit from implantation. A similar study in 2003 looked at the relationship between hearing loss and speech perception in children.21 Speech-perception results for 29 hearing-impaired children (43 ears) were compared with results for a sample of 46 children using cochlear implants. The children were of similar age (mean 9.5 years) and old enough to perform the speech-perception tests reliably. The results suggested that the CI group performed at an “equivalent hearing loss level” of around 75 dB HL (four-frequency PTA). Also, the CI group performed significantly better on all measures than the children with profound hearing loss using hearing aids.

More such data are needed to refine this process, but it does provide evidence for making decisions on audiometric information alone. Based on these data and similar information for adults, it seems reasonable to suggest that a young child with bilateral hearing levels exceeding 90 dB HL (four-frequency PTA) is likely to develop better auditory skills for speech perception with a cochlear implant than with conventional amplification. The range of 80–90 dB HL represents a gray area where a CI might provide better potential, but it may be necessary to wait a little longer and monitor the child's progress with hearing aids before making a decision.

What other evidence can be used when children are in this borderline category? As mentioned in the discussion on adults, we can be reasonably sure that an implant will provide access to the speech spectrum across all frequencies. If hearing levels are between 80 and 90 dB but aided thresholds show limited access to mid- or high-frequency speech, this is further evidence for recommending a CI.22

For very young children, differences in hearing levels between the ears will also play a part in the decision. Even when one ear has hearing in the gray area, if the other ear is much worse, this can simplify the decision. A CI in the worse ear offers an opportunity of improved auditory skills while preserving hearing in the better ear.

Middle ear disease

As in adults, middle ear disease can be a problem in evaluating infants for cochlear implantation. Not only does a conductive hearing loss component make it difficult to determine the level of sensorineural hearing loss, but also the surgery cannot proceed until the middle ear is clear. The risk of introducing infection into the inner ear which can spread to the cerebro-spinal fluid has been highlighted by recent cases of meningitis linked to CI surgery.

Multiple disabilities

Up to 40% of children with congenital hearing impairment have additional disabilities, which may include cerebral palsy, cognitive deficits, visual impairment, and severe medical conditions. Management of these children poses some of the most challenging problems in pediatric audiology.

Two main arguments arise when cochlear implantation is contemplated in this population. When funding is more readily available for implantation through health systems and/or insurance, many clinicians feel that children with multiple disabilities deserve all the help they can get. On the other hand, some would argue that with limited resources available for implant procedures, they should be applied in cases where the outcomes will be best. The best outcomes (using traditional measures) are unlikely to come from the multiply disabled population. However, the improved quality of life that even rudimentary hearing may offer such patients cannot be dismissed. There is no easy way to resolve these issues.

A primary problem in caring for a multiply disabled implant candidate is how to obtain reliable information about the extent of disabilities. This is particularly important for cognitive deficits, which are likely to affect language development. Dettman and colleagues have demonstrated that children with cognitive deficits can develop open-set speech perception, but poor outcomes are more common in this population.23 A recent study indicated a relationship between the degree of deficit and CI outcomes in a sample of 44 children with cognitive deficits.24 The benefits of an implant for children with severe or profound cognitive deficits is difficult to measure, but even in this group some sound awareness and increased responsiveness have been demonstrated.

What should be considered in evaluating multiply disabled children? First, it is important to decide if the additional problems are likely to have an impact on the outcome of cochlear implantation. For instance, visual problems are unlikely to reduce the utility of a CI, whereas others, such as cognitive deficits or poor oro-motor skills might. Additional questions to consider are: Does the child show communicative intent? Does the child respond to environmental stimuli? Might a CI do more harm than good? Often, there are no clear answers to these questions, but considering them may help in the difficult process of providing an informed recommendation to parents.

CONCLUSION

Although the application of cochlear implants has been highly successful, it is important to remain objective in providing information to potential recipients and their families. It has been demonstrated that using the distribution of speech-perception outcomes in implanted subjects to estimate the probability of success for adults and older children is worthwhile. Studies of factors affecting outcomes in adults have shown that the duration of hearing loss, the age at onset of hearing loss, and the degree of residual auditory skills prior to implantation are important considerations.

In young children, where information on speech perception cannot be obtained, audiometric information can be used to guide recommendations. For both adults and children, speech-perception data suggest that CI users have auditory skills similar to those using conventional amplification with hearing losses between 70 and 80 dB HL (four-frequency PTA).

Although there are difficult areas in the clinical application of cochlear implants, this field is one of the more successful examples of the application of technology to healthcare. A large majority of CI recipients demonstrate gains in communication skills, and often their lives are substantially changed for the better.

ACKNOWLEDGMENTS

The work described in this paper would not have been possible without the support of the Eye and Ear Hospital, Melbourne, Australia; the Cooperative Research Centre for Cochlear Implant and Hearing Aid Innovation; the staff, past and present, of the Melbourne Cochlear Implant Clinic; the School of Audiology at the University of Melbourne; and the substantial contribution made by volunteer subjects to cochlear implant research. I would like to thank Dr. Gary Rance, Dr. Shani Dettman, Dr. Karyn Galvin, Joanne Enticott, and Mansze Mok for sharing their insights.

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