Evaluating cochlear implant candidacy

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 speech perception, that make of much hearing is and have used data from a of adults with acquired deafness on to a speech-perception performance to the duration of profound hearing loss in the implanted the speech perception of hearing aid users with the of results for implanted the can the of improved performance. This provides to use in deciding whether or not to a the duration of deafness and perceptual performance for ear may help the decide which ear may be more for and have also used the of results for implanted subjects to evidence-based criteria to In this speech-perception outcomes for a group of adult CI users were In this more than used hearing to implantation and significant speech perception in at one ear. This an in the population of adults receiving implants in with the groups of were identified with significantly different speech-perception outcomes. with a pre-lingual onset of hearing loss performed than those with a post-lingual with significant residual hearing and speech perception implantation performed significantly than others with post-lingual hearing These results suggest that these groups should be when it to them about potential benefits from with auditory skills can be in the in which the potential for benefit from an implant is but the of benefit may depend on the duration of profound deafness, and other who are hearing need more It is that their be by means of accepted the must assess ear and the speech-perception to determine the level of benefit from conventional amplification, the in performance for the two and the level of then is an evidence-based the of post-implant results, and showed that of implant users for at their 3-month Based on this candidates best at a chance of improvement with an implant. criteria were for other of speech perception, including and perception in But about those who do not The of for a group of adult CI recipients with useful residual hearing. implantation who than the have at a chance of improvement with a cochlear the The showed a for outcomes to the potential benefit for implant However, an informed consent process must also when A chance of improvement a chance that performance will For if the ear considered for implantation for with conventional amplification, this hearing is likely to be by the implant If the CI provides results, the candidate may be there are usually two to and their speech-perception performance often So, it appear that a is for the implanted ear in to the for performance. level of speech-perception performance in the ear to be implanted provides of we can to the post-implant results that a of or for is by of implant users in the residual hearing So, if the ear to be implanted criteria can be for other the chance of performance with a CI is than These have the of the approach followed in over the for post-lingual adults performance with conventional is than for criteria for other and performance for the ear to be implanted is then candidates can be informed with confidence that there is a chance of improved performance and than chance of performance. In the there is the potential loss of the and the possible of speech perception on the implanted from to that this approach always the ear speech as the ear to be implanted in this group of The applied these criteria from to with adult subjects receiving implants the these subjects perception and in their and one ear with a subjects were implanted in the ear. the showed improved speech perception with their CI over their performance but one patient showed improved speech perception with their implant with the performance in that ear. These results closely with the expected outcomes based on of the of results, and they provide good for the of this The point for almost all of the auditory system is the Although recommendations about cochlear implantation should always be based around speech-perception results, the and can provide additional useful information. and have that adults with hearing in the and to profound show a of speech-perception In this there were with a hearing loss to who well for and benefit from a cochlear implant. to for We must be of these and not a patient's on the However, there is a significant of hearing loss and speech perception, and it is this in the information. study and additional information in the of implant candidates show the hearing loss and perception in and in and hearing loss for adult hearing aid users. The line the for perception in The line the for in from on the speech-perception for adult CI recipients are on the The data suggest that CI recipients have speech-perception ability similar to that of hearing aid users with in the of to results for CI recipients are these and show a similar and to hearing aid users with and not decide whether or not to a CI on the information but these results do provide a to which subjects should be considered for further and they help identify those who are with conventional amplification. This of information it to that cochlear implants may be for any patient bilateral hearing loss hearing is than this rather there may be a CI be but only speech perception is much than expected based on the of auditory The can also provide useful information for the evaluation, but there are many A effort is required to establish that the hearing used are for the hearing loss and that they have been and to accepted that the are a useful is to the patient's ability to speech information in the and higher to 4000 It is well with CIs provide good to speech across this This can then to other for the of the benefits of with a We now over into and issues that may affect I will not into on these but I will summarize some key audiologists need some and often an important of hearing loss the of hearing loss is not often but some as ear cochlear and provide other of post-lingual the of that affect the required for cochlea we are at and these There are audiologic and for many of the etiologies. ear is a for implant surgery, as it raises an unacceptable of infection or Audiologists need to surgeons in ear as they to the This may surgery and to months of the implant surgery Cochlear often the of of the This can be observed on and may the of the electrode array or make it In these patients an increased that stimulation will affect the nerve at some This auditory but it is a in the informed consent pathologies are difficult to identify in patients for cochlear assessments at these pathologies on some residual hearing. will any and the surgery for may the use of a cochlear implant for that ear. more of may effects on the auditory and due to surgery, or or These individual and from the clinical In some stimulation of the may help establish if there may be benefit from an implant. patients the there has been much of the effect of age on potential risks and benefits of cochlear implantation, and of whether or not age should be a for the the age has from to to and it now appears there is no age should there be an age factors may be We have that CI patients have speech-perception patients are more likely to have problems that could increase the of the providing to patients has a greater because they are likely to A recent study of outcomes for patients only implant users over and there is that any in the may over time. there is for the that patients should not a cochlear implant because they do not do as The risks for many For an the of major to be as as the potential benefits that many patients may if surgeons and must the and of in this studies have the effect of CI surgery on residual in the implanted In patients who have in the implanted there is a significant chance of Some patients in the and this with in of and In most the over a of but the is sometimes more Although suggest that changes in are similar for and a of patients have This is consistent with neural in the group to The is by the that patients are more at of due to and It is that for CI patients due be to the of and the of the if it with hearing loss are more to and than the The decision to CI surgery and the actual are on the of a are the and that the implant will and the that recipients often when they use their speech processor. Audiologists and others who with patients should take an approach to these and be to when there is of a CI benefit from a with in hearing loss and to of hearing loss Because of the to cochlear it is not for hearing-impaired adults to the that a will be than their current hearing their of hearing Prospective patients are sometimes of the of hearing loss and level of speech perception that them into for In they may their and on speech-perception This is not as as one and some of these patients may not be as the clinicians are on them for the Therefore, audiologists should for any among communication observed communication and speech-perception performance. as acoustic if potential can most of these There are also the of people with hearing to a cochlear implant. if the of the is these will be But there are some CI recipients there who should have been ADULTS WITH HEARING LOSS by et adults with pre-lingual onset of bilateral hearing loss more than those with acquired deafness. from this in expectations, similar techniques can be applied to this group as We can use the of outcomes within this group to with individual speech-perception with conventional to the probability of Studies of children and with CIs suggest additional factors that can provide on speech-perception Language development, as by a duration of profound hearing loss, and pre-operative speech-perception performance were significant predictive factors for speech-perception outcomes. The work of Blamey and has the development and the potential for speech perception with a cochlear implant hearing comprehensive study of hearing-impaired children showed that development was a of speech-perception ability than any other in the including of hearing loss or age at or speech-perception ability for deaf adults and children is an of their ability to process auditory information for speech If they significantly on an speech their limited it is a that they will be to use CI input If their speech perception is useful residual they may have processing the implant In evidence-based recommendations are possible for pre-lingually deaf adults based on the of implant outcomes for this group and of their hearing development, and use of residual hearing. In children, the benefits of implantation for speech perception and development of and speech production are well not that implantation improves the of outcomes. we a strong children as as In the CI will with children and and the of hearing will into the first months of speech perception to decide if a should be implanted will usually be as most children will be in the of and cognitive For these we need to ask, is the potential to auditory skills with a CI significantly than the potential with conventional This is difficult to in children. We use with adults and children to these For children as as it should be possible to use techniques to determine and optimum The of the information is as it will about We now have a of hearing that can hearing at any age. These the and auditory Although these assessments provide there is always a of and that used to audiologists is the of auditory in which neural appear to be but there is of cochlear is now a and CIs have been used with people with However, this is only one possible of results that could that is may be as as a It is difficult to implantation both and a consistent level of hearing I data on the hearing loss and speech perception in adults and the results for CI patients this to provide a to the of hearing loss that may benefit from A similar study in at the hearing loss and speech perception in results for hearing-impaired children were with results for a of children cochlear implants. The children were of similar age and to the speech-perception The results that the CI group performed at an hearing loss of around the CI group performed significantly on all than the children with profound hearing loss hearing aids. data are to this but it does provide for making on information Based on these data and similar information for adults, it to suggest that a with bilateral hearing is likely to auditory skills for speech perception with a cochlear implant than with conventional amplification. The of a a CI provide but it may be necessary to a and the with hearing making a decision. other can be used when children are in this in the on adults, we can be reasonably sure that an implant will provide to the speech spectrum across all If hearing are and but show limited to or speech, this is further for a For children, in hearing the will also a in the decision. when one ear has hearing in the if the other ear is much this can the decision. A CI in the ear an opportunity of improved auditory skills hearing in the ear. Middle ear in adults, ear can be a in evaluating for cochlear only does a hearing loss make it difficult to determine the level of hearing loss, but also the surgery cannot the ear is The of infection into the inner ear which can to the has been by recent of to CI to of children with hearing have additional which may cognitive and conditions. of these children some of the most problems in when cochlear implantation is in this is more available for implantation through systems many clinicians that children with all the help they can On the other hand, some argue that with limited available for implant they should be applied in the outcomes will be The best outcomes are to from the However, the improved of that hearing may patients cannot be There is no to these issues. A in for a implant candidate is how to information about the of This is particularly important for cognitive which are likely to affect and have that children with cognitive can speech perception, but outcomes are more in this A recent study a the of and CI outcomes in a of children with cognitive The benefits of an implant for children with or profound cognitive is difficult to but in this group some and increased have been should be considered in evaluating it is important to decide if the additional problems are likely to have an on the of cochlear For problems are to the of a as cognitive or skills questions to are: the show the to a CI do more than there are no answers to these but them may help in the difficult process of providing an informed to Although the application of cochlear implants has been it is important to in providing information to potential recipients and their families. It has been that the of speech-perception outcomes in implanted subjects to the probability of for adults and children is Studies of factors affecting outcomes in adults have shown that the duration of hearing loss, the age at onset of hearing loss, and the of residual auditory skills to implantation are important considerations. In children, information on speech perception cannot be information can be used to recommendations. For both adults and children, speech-perception data suggest that CI users have auditory skills similar to those conventional with hearing and Although there are difficult in the clinical application of cochlear this is one of the more of the application of to A of CI recipients in communication skills, and often their are changed for the The work in this paper not have been possible the of the and the for Cochlear and the and of the Cochlear the of at the of and the by subjects to cochlear implant I to and for their