This installment of the Tot Ten discusses some of the most significant developments in cochlear implant technology and services for children.
10. TURN DOWN FOR WHAT?
It's well-known that both children and adults with cochlear implants experience difficulty with speech recognition in noise. Cochlear implant manufacturers have responded by developing signal processing strategies shown to improve comfort, sound quality in noise, and speech recognition.
Furthermore, cochlear implant manufacturers are beginning to introduce acoustic scene classification technology, which analyzes the acoustics of the input signal, classifies the environment into one of several categories (e.g., speech in quiet, speech in noise, wind noise, music, etc.), and automatically selects signal processing features designed to optimize performance for the given environment.
9. GETTING OBJECTIVE WITH ANSD
Clinicians are often faced with difficult decisions in the management of children with auditory neuropathy spectrum disorder (ANSD). Namely, it is difficult to determine how hearing aids should be fitted to infants and young children because auditory brainstem response (ABR) results do not correlate with behavioral threshold.
Although many children with ANSD are better served by cochlear implantation, some do develop adequate spoken language abilities with hearing aid use. The process of subjectively determining who needs an implant often requires a substantial period of time, which delays implantation for those who need it. Fortunately, researchers and clinicians are developing and identifying objective measures of auditory function.
Harvey Dillon, PhD, and colleagues; as well as Gary Rance, PhD, and Anu Sharma, PhD, have all demonstrated that the presence of a cortical auditory evoked response is an objective signal that auditory stimulation is being provided to the auditory cortex.
Further, Dr. Dillon and the National Acoustic Laboratories (NAL) team have used cortical auditory evoked potential (CAEP) assessment as an indicator of audibility for low-, mid-, and high-frequency speech sounds, and as a method to fit hearing aids for children with ANSD.
Researchers are also employing the CAEP to determine whether children with auditory neuropathy spectrum disorder are likely to develop adequate speech recognition with hearing aids. Patricia Roush, AuD, and colleagues at the University of North Carolina have shown that cortical auditory responses in the acoustic change complex may be useful in differentiating between children with ANSD who will benefit from hearing aids and those who need cochlear implants.
Likewise, Anu Sharma, PhD, and her team of researchers at the University of Colorado at Boulder have shown that the extent of coherence of the CAEP response across multiple single sweeps indicates synchronicity of auditory function in the cortex. Children with higher degrees of synchronicity may be more likely to benefit from amplification, while those with lesser degrees should be considered for cochlear implantation.
Our field has been slow to adopt CAEP measures for the routine assessment of pediatric auditory function. This trend will likely change.
8. ROLE OF THE RADIOLOGIST
Historically, CT scanning has been used to evaluate the anatomy of the temporal bone, informing decisions about the insertion of the cochlear implant electrode array.
However, Craig Buchman, MD, and colleagues at the University of North Carolina recently demonstrated the need to use MRI to evaluate the integrity of the auditory nerve in children with ANSD, and in those with no responses to acoustic stimuli on ABR or auditory behavioral assessment.
Some of these children may have deficient or absent auditory nerves, Dr. Buchman showed. Consequently, they will receive little to no benefit from cochlear implantation. Auditory nerve aplasia cannot be revealed by CT, so MRI should be considered mandatory for children with ANSD or minimal responses to audiologic measures.
With that said, CT is a valuable tool for cochlear implant programming. René Gifford, PhD, and colleagues at Vanderbilt University, and Laura Holden, AuD, and the team at Washington University School of Medicine in St. Louis, have shown that postoperative CT scans may be used to indicate the position of the electrode contacts in the cochlea.
This information may then be used to determine which electrodes should be disabled because they may cause channel interaction or are in an unfavorable position relative to the modiolus. Although this work is still within the research arena, it appears to hold great promise.
7. DATA LOGGING ESSENTIAL
Over the past year, data logging has found its way into cochlear implant sound processors. Although published studies haven't yet examined its utility in pediatrics, anecdotal experience indicates that data logging is one of the more significant recent developments for the management of children with cochlear implants.
Cochlear implant teams go into “red-alert mode” when their pediatric patients make limited speech and language progress. The potential reasons for this outcome are quite varied, and the cochlear implant team must quickly identify the cause in order to facilitate optimal outcomes. Data logging has been extremely valuable in identifying two of the culprits.
Anecdotally, insufficient wear time is one of the primary reasons for limited progress. Young children with cochlear implants should be using their devices for at least 10 hours per day, whenever they are awake.
We also must ensure that children are exposed to sufficient intelligible speech. Psychologists Betty Hart, PhD, and Todd Risely, PhD, found that children ideally should be exposed to 45 million words by the time they are four years old. (Meaningful Differences in the Everyday Experience of Young American Children. Baltimore, MD: Paul H. Brookes Publishing; 1995.) Contemporary data-logging systems indicate not only the number of hours a child uses a cochlear implant, but also the estimated hours during which the child is exposed to speech.
The audiologist should share this information with the child's auditory–verbal therapist, particularly when data logging suggests insufficient exposure to speech. The therapist can then suggest strategies to promote a more enriching environment for speech and language development.
6. CI FOR SSD?
We have long known that children with single-sided deafness are at risk for academic challenges, speech and language delay, and psychosocial deficits.
Although bone-anchored implantable hearing devices and contralateral routing of offside signals (CROS) hearing instruments are helpful in overcoming the head shadow effect, they offer little to no benefit for localization. Additionally, they provide no stimulation to the poorer ear, leading to abnormal development of the auditory nervous system.
While there is a paucity of published studies supporting cochlear implantation for children or adults with single-sided deafness, initial reports presented at professional conferences have largely been promising.
5. EAS TO NAVIGATE THE SLOPES
Pediatric audiologists are fully aware of the challenges involved with fitting hearing aids for children with normal to near-normal low-frequency hearing and precipitously sloping, severe to profound high-frequency hearing loss.
Oftentimes, it is difficult or impossible to provide sufficient audibility and identification of high-frequency speech sounds. Furthermore, we must attempt to keep the ear canal largely un-occluded in order to preserve the interaural low-frequency cues that are critically important for localization and speech-in-noise understanding.
Provision of an open-fit hearing device and consistent audibility of mid- and high-frequency speech cues are mutually exclusive and often unobtainable goals for children with this audiometric configuration.
Hybrid cochlear implantation (electric–acoustic stimulation) has been shown to provide substantial improvements in localization as well as speech recognition in quiet and in noise for adults with precipitously sloping severe to profound high-frequency hearing loss.
Bruce Gantz, MD, and colleagues at the University of Iowa recently initiated trials to explore the benefits of hybrid cochlear implantation for children with severe to profound high-frequency hearing loss. This technology will likely become the standard of care for this patient population.
4. IT BEGINS IN THE OR
Ten years ago, it was often said (probably at least partially in jest) that the cochlear implant surgery was the easiest part of the child's cochlear implant journey. The hard work was the programming of the implant and the hours of therapy required after the surgery.
Without a doubt, the audiology and auditory–verbal therapy components are fraught with “blood, sweat, and tears,” but we are also now fully aware of the critical role the surgeon plays in the child's outcome.
Numerous researchers and clinicians have demonstrated the importance of inserting and maintaining the electrode array in the scala tympani of the cochlea. When the electrode array dislocates to the scala vestibule, higher stimulation levels are needed from the cochlear implant, which probably leads to greater channel interaction and distortion. Furthermore, cross-turn stimulation is more likely.
Second, when the electrode array leaves the scala tympani and perforates through the delicate structures in the scala media, the sensory and supporting cells of the organ of Corti are damaged and most likely destroyed.
As a result, degeneration of the auditory nerve fibers becomes more likely, which may eliminate the child's opportunity to benefit from future advances in medical inner-ear therapies.
3. HOW LOW SHOULD WE GO?
Cochlear implants have long been considered the technology of choice for children with profound hearing loss. However, recent research has suggested that many people with severe hearing loss will likely perform better with cochlear implants than with hearing aids.
Dr. Dillon; Teresa Y.C. Ching, PhD; and colleagues from NAL's Longitudinal Outcomes of Children with Hearing Impairment (LOCHI) study have shown that children with cochlear implants achieve auditory, speech, and language abilities on par with a child who wears hearing aids and has a four-frequency pure-tone average of 66 dB HL.
This work suggests that cochlear implants should most likely be considered for many children who have hearing thresholds better than the profound range. Publications coming from the LOCHI study indicate that many children are receiving cochlear implants when their hearing loss meets or exceeds 75 dB HL.
When children fall on the “audiometric fence” between cochlear implant and hearing aid candidacy, the most important factors to consider are the child's speech-recognition capacity and functional speech, language, and auditory development, as well as the family's desired outcomes. When functional development does not appear to be adequately supported by hearing aids, cochlear implantation should be considered.
2. LISTEN TO THE RADIO
Although cochlear implant technology is fantastic, we also know that most children with cochlear implants struggle in noisy situations.
Research conducted by Imran Mulla, PhD, has shown that infants and toddlers routinely function in environments with signal-to-noise ratios (SNRs) ranging from 0 to −15 dB. Unfortunately, no cochlear implant technologies can support adequate speech recognition under these circumstances.
On a positive note, cochlear implant recipients can perform quite well in real-world environments with the use of wireless (radio) remote-microphone technologies.
Cochlear implant manufacturers recently introduced several types of wireless accessories that stream audio signals directly to the cochlear implant sound processor. As audiologists, we should do everything in our power to ensure that every child we serve is equipped with wireless remote microphone technology.
1. EARLY BIRD GETS THE WORM
Recent findings from the LOCHI study underscore the importance of early implantation. Dr. Ching and colleagues examined speech, language, and auditory outcomes in children with hearing aids or cochlear implants, and showed that the age at which a child received a cochlear implant was one of the most important factors influencing outcome.
In fact, speech, language, and auditory outcomes decreased by almost one-half of a standard deviation when implantation was delayed from 6 months to 12 months of age. Another half standard-deviation reduction in speech and language outcomes was found when implantation was further delayed from 12 months of age to 18 months. These findings have enormous implications.
The United States Food and Drug Administration calls for the consideration of a cochlear implant when a child reaches his or her first birthday. Obviously, the LOCHI findings suggest that waiting until that time to provide a cochlear implant for an infant with a severe to profound hearing loss possibly will limit the child's progress.
Cochlear implantation should be considered at 6 to 9 months of age for children with severe to profound hearing loss, particularly when the speech–language pathologist and the child's family suggest limited benefit from hearing aids. Sooner rather than later is critical when early brain development is at stake.© 2014 by Lippincott Williams & Wilkins, Inc.