Who exactly is a cochlear implant candidate? Well, that question doesn't have a simple, straightforward answer.
Cochlear implant candidacy criteria have evolved dramatically since multichannel implants were first approved for adult use by the FDA in 1985 and in 1990 for the pediatric population. Initially, only individuals with bilateral profound sensorineural hearing loss with no open set speech recognition were considered candidates for cochlear implantation. Over time, however, these criteria have become less stringent and we are now implanting individuals with greater amounts of residual hearing and pre-implant speech recognition scores.
Speech recognition outcomes have been climbing steadily since the earliest reports following multichannel implantation.1–6 Part of this improvement is attributed to advancements in technology both with the internal device as well as for the externally worn processors.
Another portion of this improvement can be attributed to the advancements in speech coding strategies (e.g., how the incoming signal is transformed from the complex acoustic waveform to the electrical stimulation of auditory nerve fibers via the intracochlear electrodes). Liberalized criteria for implantation and the fact that we are now implanting individuals with considerably more residual hearing, higher preoperative speech perception scores, and shorter durations of severe-to-profound deafness, also play a role in this improvement, and there may be other variables that we haven't even considered.
Cochlear implants have been shown to literally transform the lives of recipients in a way such that they have been labeled as the most successful and effective implantable prosthesis in terms of restoring function to recipients.7 Thus the purpose of this article is to provide a review of current cochlear implant criteria for adults and children so that a broader range of hearing health professionals are able to identify those individuals who may be able to take advantage of this technology.
CANDIDACY CRITERIA: THE BASICS
Until recently I have always asked prospective cochlear implant audiologists, AuD externs, and student clinicians the question, “What are the current cochlear implant criteria for adults and children?” The reason that I have discontinued asking this question in interviews is that, to date, not a single individual has answered correctly—at least not entirely.
The determination of cochlear implant criteria has multiple elements dealing with audiometric threshold, speech recognition performance, age, auditory progress with hearing aids, and the list goes on and on. Further clouding the issue is that there are three cochlear implant companies that hold FDA approval to market their devices within the United States—Advanced Bionics, Cochlear Limited (Cochlear Americas), and Med El—all of which have different labeled indications for implantation.
FDA labeled indications refers to those specified criteria for which a manufacturer intends to market their product. Each cochlear implant system is shipped with a “Physician's Package Insert” which specifies the FDA labeled indications for implantation. Since the three cochlear implant manufacturers generally work independently, the labeled indications for cochlear implant criteria vary across the companies. The current cochlear implant criteria—as of June 2011—are described below.
Adult implant candidates
Adult cochlear implant candidacy criteria vary not only amongst implant manufacturers but also with insurance carriers (private commercial insurance vs. Medicare coverage).
With respect to audiometric thresholds, both Advanced Bionics and Med El specify bilateral severe-to-profound sensorineural hearing loss for adult implant candidacy. On the other hand, Cochlear Americas and Medicare specify bilateral moderate-to-profound sensorineural hearing loss—recognizing that individuals with sloping hearing losses will not always obtain the benefit from amplification needed to achieve successful communication.8Figure 1A displays the evolution of audiometric criteria over the years to the most current encompassing region of audiometric thresholds for moderate sloping to profound sensorineural hearing loss.
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Figure 1: Illustration of the evolution of audiometric criteria over the years.
Aside from audiometric threshold, perhaps the more definitive component of determining adult implant candidacy involves speech recognition testing. As many of us recognize, individuals with significant hearing loss often report that they are unable to adequately “hear” someone unless they are looking directly at them. Thus, they are relying heavily—if not entirely—on visual cues such as lip reading and nonverbal signals for communication. In determining cochlear implant candidacy, in order to gain an understanding of an individual's auditory-based speech recognition abilities, speech materials are presented without visual cues.
Just as important as presenting speech stimuli without visual cues is the presentation of recorded materials for the assessment of speech recognition abilities. Roeser and Clark evaluated monosyllabic word recognition using both recorded stimuli as well as monitored live voice (MLV) for 32 ears.9 They reported that word recognition scores for MLV and recorded stimuli were significantly different for 23 of the 32 ears (72%), with the difference between the scores being as high as 80 percentage points—with the scores obtained via MLV being higher in every case.
These results show that using MLV presentation of speech stimuli for determining cochlear implant candidacy will likely exclude a large proportion of individuals who may actually have met candidacy criteria using standardized recorded materials. Furthermore, Cochlear Americas, Med El, and Medicare all specify the use of recorded stimuli for the implant evaluation.
Yet another consideration for the administration of speech recognition materials is the presentation level for determining candidacy. Historically, stimuli were presented at 70 dB SPL in the sound field. The problem with this is that 70 dB SPL is not representative of average conversational speech. Pearsons et al. reported that average conversational speech levels were 60 dB SPL.10
A number of studies have examined the effect of presentation level on speech recognition outcomes for individuals with cochlear implants and those who may be cochlear implant candidates.3,11,12 They found that post-implant speech recognition was essentially identical for 60 and 70 dB SPL, but that pre-implant performance was significantly poorer for 60 dB SPL as compared to 70 dB SPL.
Consequently, using 70 dB SPL as the presentation level for determining implant candidacy puts the patient at a disadvantage because (1) it is not representative of average conversational levels in the real world, (2) it has the potential to artificially inflate one's speech recognition performance, and (3) it could potentially disqualify an individual from candidacy who could derive significant benefit from cochlear implantation.
As far as the speech recognition material to be used for determining implant candidacy, again there are differences across the manufacturers. As of June 2011, Advanced Bionics specified sentence recognition up to 50 percent in the best aided condition.13 Cochlear Americas specified sentence recognition—no particular material specified—up to 50 percent correct in the ear to be implanted and up to 60 percent in the best aided condition. Med El listed HINT sentence recognition up to 40 percent correct in the best aided condition, and lastly, Medicare criteria are also outlined independently to include sentence recognition performance up to 40 percent correct in the best aided condition—no material specified.
Though these criteria are included in the current FDA labeled indications for the three manufacturers, the implant companies have recently come together to determine a recommended test battery for both pre- and post-implant assessment of performance which includes AzBio sentences,14–15 BKB-SIN sentences in noise,16,17 and CNC monosyllabic words.18
Having a test battery consisting of words, sentences in quiet, and sentences in noise provides information on an individual's performance in a variety of listening conditions as well as verification of subject performance via cross-checks across the speech recognition materials given the known inter-relationship of individual performance across those measures.6,19
For those clinicians who do not assess speech recognition performance at a calibrated level of 60 dB SPL in their clinic—which will likely be most clinicians not engaged in cochlear implant clinical responsibilities—the question is often posed, “How do I know when to refer an adult patient for a cochlear implant evaluation?” It is often the case that the audiogram alone provides a poor indication of functional communication ability with well-fitted hearing aids for average conversational level speech.
In other words, similar audiograms do not necessarily yield similar levels of benefit from appropriately fitted hearing aids.20–22 Thus it is important to rely on patient report. Is your patient able to talk on the phone? If they report that they can no longer talk on the phone or if they are only able to talk to very familiar individuals on the phone (such as a spouse, sibling, child, or friend), this is a good indication for cochlear implant referral. Does you patient report that they are no longer attending social functions? This is also a good indication for referral.
It is important to note that a cochlear implant referral does not necessarily equal a lost hearing aid patient. There are an increasing number of studies demonstrating that individuals making use of a cochlear implant and a contralateral hearing aid (also referred to as bimodal listening) are able to integrate the electric and acoustic signals to derive significant benefit for speech recognition in quiet and in noise23–27 as well as for the recognition of music.28– Thus the bimodal listener can continue to be a unilateral hearing aid patient for years to come.
Pediatric implant candidates
Cochlear implant criteria for children are considerably more complicated with many more elements of candidacy, including age, audiometric thresholds, auditory progress with hearing aids, speech recognition performance (for older children), and etiology, etc.
Starting with audiometric threshold, for children aged 12 to 24 months, the current criteria specify bilateral profound sensorineural hearing loss. It is important to note that this indication does not imply that children with less severe hearing loss do not benefit from cochlear implants. Historically, the greatest concern was that establishing behavioral thresholds was most difficult for the youngest children; thus the criteria for the youngest candidates happen to be most stringent. Given our current array of behavioral and objective measures to serve as audiologic checks and balances, this concern may not be as valid as it once was.
Notwithstanding the labeled indications for bilateral profound sensorineural hearing loss for children under 2 years of age, during the hearing aid trial, children should be making at least month-to-month auditory progress and well as speech and language developmental progress. In other words, if a child has been fitted with hearing aids for 3 months, they should make at least 3 months of progress in auditory skills and speech/language development. If this is not the case for a child making full-time use of amplification and appropriate intervention, then a cochlear implant evaluation should be considered.
For children 2 years of age and older, current audiometric criteria for implantation are slightly more lenient, including bilateral severe-to-profound sensorineural hearing loss. Again, if a child has less severe sensorineural hearing loss and is not making auditory progress with full-time use of well-fitted hearing aids and recommended intervention, referral for a cochlear implant evaluation is appropriate.
The evaluation of auditory skills and progress for children aged birth to 2 years (the first defined age period for determining cochlear implant candidacy) is not achieved by simply looking at the audiogram. Auditory skills are generally assessed via parental history and administration of validated questionnaires designed to gauge auditory-based responsiveness to speech and sounds in a child's environment.
Though any validated questionnaire would be considered appropriate for gauging auditory skill development, one of the most frequently cited and clinically administered questionnaires used for children from birth to 3 years is the Infant-Toddler version of the Meaningful Auditory Integration Scale (IT-MAIS).31 All three manufacturers reference the MAIS and/or IT-MAIS for use in determining auditory progress with amplification.32 The 10-item IT-MAIS is frequently used due to the widespread familiarity, free and public availability, as well as the ease and time required of administration (approximately 10 minutes).
There are also a number of other parental questionnaires that can be used to assess spontaneous and prompted responses to auditory stimuli for infants and toddlers, including the 35-item LittlEars auditory questionnaire;33,34 the 23-item Functioning after Pediatric Cochlear Implantation (FAPCI) questionnaire;35 Functional Auditory Performance Indicators;36 and the Early Listening Function questionnaire. Of course, implant candidacy cannot be based solely on the results of auditory questionnaires. Speech and language evaluations completed by speech/language pathologists with childhood hearing loss experience and expertise are absolutely critical, as well. In addition, regular therapy should be considered a part of the hearing aid trial for all children being seen for implant evaluations.
As is the case with infants and toddlers, assessment of auditory skills for preschool-aged children cannot always be well predicted by the audiogram. Behavioral assessment of auditory skills, including speech recognition skills, should always be attempted for preschoolers. Due to a number of potential factors, speech recognition testing may not be possible or only limited information may be obtained; therefore, there are also a number of validated auditory questionnaires appropriate for use with preschool children. Some of the more popular and widely used questionnaires include the MAIS, PEACH (Parents' Evaluation of Aural/Oral Performance in Children), and the FAPCI.37
The determination of cochlear implant candidacy for older children is generally based upon either mono- or multi-syllabic word recognition—depending on which metric is most developmentally appropriate. The speech recognition materials that are specifically listed by the cochlear implant manufacturers in the Physician's Package Insert include the Early Speech Perception test,38 the Multisyllabic Lexical Neighborhood test and the Lexical Neighborhood Test,39 the Phonetically Balanced Kindergarten (PBK) word recognition test,40 and HINT sentences for children (HINT-C).41
As far as the FDA labeled candidacy criteria for older children, pre-implant word recognition performance ranges from 12-30% correct in the best aided condition across the three manufacturers. Advanced Bionics further lists performance up to 30% correct for HINT-C sentences—when developmentally appropriate for children over 4 years.
The need for the expansion of pediatric cochlear implant criteria has been and remains a hot topic in the field. There are a number of studies suggesting a relatively narrow critical period for cochlear implantation for the development of listening and spoken language.42–50
FUTURE DIRECTIONS
Up to this point, the focus has been conventional cochlear implant criteria. There are, however, more and more individuals who are receiving cochlear implants with the aim of preserving low-frequency acoustic hearing. This type of cochlear implant is often referred to as a hybrid cochlear implant or as combined electric and acoustic stimulation (EAS).
The preservation of acoustic hearing with cochlear implantation can be achieved with short, specifically designed EAS electrodes such as the Nucleus Hybrid series,51,52 the Med El Flex EAS series implants,44 or even with a conventional long electrode array.53–56 When successful, the preservation of acoustic hearing with cochlear implantation allows for the combination of electric plus binaural acoustic hearing. To date, there are a number of reports demonstrating significant EAS speech perception benefit for complex listening conditions.57–59
Though only available via clinical trial in the United States with a short electrode, Figure 2B displays the audiometric inclusion criteria for Hybrid/EAS cochlear implantation. As shown in the figure, audiometric thresholds may be within the range of normal up to approximately 60 to 70 dB HL through 750 Hz, and must be no better than 70 dB HL from 1500 Hz and above. Many readers may be thinking that these criteria overlap with hearing aids and middle ear implants—which happens to be true. For these individuals with relatively good low-frequency hearing and precipitously sloping high frequency sensorineural hearing loss, it is currently unclear what the best treatment option is.
Figure 2: Illustration of the audiometric inclusion criteria for Hybrid/EAS cochlear implantation.
A number of research labs across the world are currently studying this very issue. Of course, the very best way in which to research the answer to this question would be a randomized, double blind clinical trial for hearing aids, middle ear implants, and Hybrid/EAS cochlear implants. For obvious reasons, the blinding component is completely impossible to achieve and the randomized selection of treatment would likely be considered too controversial for more research institutions and perhaps even unethical, as well. Thus the research coming out over the next few years will likely weigh in on what may serve to be the gold standard treatment recommendation for this population of patients.
A COLLECTIVE PROCESS
Cochlear implant criteria are not necessarily straightforward for either adults or children and the topic of assessing candidacy could fill the pages of an entire book. Other topics of great interest and high clinical relevance include bilateral cochlear implantation versus bimodal listening, thus we have only begun to scratch the surface in this article.
The determination of cochlear implant candidacy is truly a process that is accomplished via the collective teamwork of a multi-disciplinary group of professionals, including audiologists, speech-language pathologists, deaf educators, social workers, radiologists, and of course, otologists and neurotologists.
Given the tremendous communicative benefit afforded by cochlear implants, and the outline of current cochlear implant criteria provided here, the goal of this article is to help practitioners feel more knowledgeable about who might be a candidate for cochlear implants and when might be the appropriate time to refer for evaluation. Of course as criteria continue to expand and we continue to see greater numbers of patients with preserved hearing following cochlear implantation, the cochlear implant selection process will continue to evolve.
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