Cochlear implantation in children with cognitive impairments

Abstract

Cochlear implants allow children with severe to profound hearing loss to gain access to sound. This should be true regardless of the child's cognitive function, and yet there is some hesitancy about providing cochlear implants to children with cognitive delays or impairments. Hearing loss may be accompanied by cognitive deficits in the presence of a recognized syndrome (e.g., CHARGE or Trisomy 21) or after infectious etiologies including meningitis and cytomegalovirus. It is very difficult to assess the presence or degree of cognitive delay in infants, but, for toddlers and children, delays in cognitive development may already have been diagnosed by the time a referral for hearing testing is made. In some cases, the audiologist might raise a suspicion of cognitive impairments based on clinical observations, including the child's inability to provide reliable behavioral responses to sound or vibrotactile stimuli using age-appropriate audiometric measures (despite multiple attempts). Determining the potential risks and benefits of cochlear implantation can be more difficult in children who do not have age-appropriate cognitive skills, making the assessment of candidacy for cochlear implantation challenging in some cases. In this article, we will discuss factors that must be considered when deciding whether or not to provide a cochlear implant to such children. In some circumstances, cochlear implantation may not be recommended for children with cognitive delays. This decision will involve an assessment of the risks of cochlear implantation as well as an effort to predict expected outcomes. DEFINING RISKS OF IMPLANTATION Any family considering cochlear implantation for their child must be made aware of the risks of the surgery. Moreover, children who are able to assent to treatment themselves must do so. In the case of an older child who may have cognitive impairment, it is essential to determine if the child can give assent for cochlear implantation. It is also important to identify any concerns the child may have regarding this procedure. It is our responsibility to provide information about the potential short- and long-term risks to the family and, if appropriate, to the potential recipient. First, we must determine if cochlear implantation will damage residual hearing that could be used with or without hearing aids. This can be difficult to determine in children with cognitive delays who, like very young children, may be unable to provide reliable responses to sound in behavioral audiometric assessments. In such cases, we can use objective measures of auditory function (e.g., otoacoustic emissions, electrophysiological measures, stapedius reflexes) combined with a period of hearing aid use to monitor any progress in the child's hearing ability. Whenever possible, this monitoring is best done by a team of people who closely observe the child, including parents, caregivers, teachers, and therapists. Secondly, the risks of surgery must be discussed. These include intra-operative risks related to anesthesia and the implant surgery itself, as well as post-operative risks such as bleeding and infection. Longer-term risks include the potential for the device to malfunction and for removal to be required sometime during the patient's lifetime. Identifying device failure might be more difficult in children with cognitive impairments than in peers with more typical development of skills. This is because a problem related to the implant is often discovered when the user complains about his or her hearing with the device or the family notices a decrement in hearing or speech. There is a greater risk of missing a problem related to malfunctioning of the cochlear implant in a child who is unable to indicate that he/she is experiencing unusual hearing sensations or difficulties. This is also true of very young children. One of our options is to ask the educators and therapists who interact with the child frequently to indicate or confirm if they have noticed a negative change in hearing performance or noticeable slowing of progress. However, a potential problem with this approach is that it assumes that the same people are consistently involved in the child's education, care, and services. While we can insist on a period of trial therapy with hearing aids prior to cochlear implantation to assess the child's use of residual hearing, it is not feasible to mandate these services, which are not typically provided by the cochlear implant program, throughout the long term of cochlear implant use. Thus, we should consider if the risk of missing a potential device failure is reasonable for any particular child given the potential benefits of implantation for that child. This also speaks to the need for continued communication between all those involved in the child's care and education throughout his or her life. Finally, we try to ensure that there is absolutely no risk of providing uncomfortable stimulation through the cochlear implant. In our clinic, we use physiological measures to assess loudness and loudness growth evoked by electrical stimulation (i.e., electrically evoked responses from the auditory system and the electrically evoked stapedial reflex).1,2 We can also use electrophysiological measures to identify non-auditory stimulation3-5 and to help guide how we set the electrical stimulation provided from the cochlear implant.1,6,7 However, we need children to provide behavioral responses to noxious or unpleasant sensations from the cochlear implant so that we can change the stimulation parameters if needed to eliminate any discomfort. If we are concerned during candidacy assessment that a child may be unable to provide this behavioral feedback, we suggest that it is currently unsafe to provide that child with a cochlear implant. This ability can be reassessed as the child ages, but we would always prefer to limit the duration of deafness prior to implantation. Future methods of testing implant performance may be able to reduce the chance of providing unwanted stimulation from the device. PREDICTING BENEFITS OF COCHLEAR IMPLANTATION Many, but not all, of the risks discussed are considered reasonable to undertake if the child's potential for acquiring hearing is good. In some centrers, such as ours, we also expect that better hearing will allow the child to develop usable oral speech and language. Unfortunately, it can be very difficult to predict outcomes in children with multiple disabilities including cognitive impairment. Some work has been done in this area and the general feeling is that most children with cognitive delays show improved hearing with some speech perception, but that their skills lag behind those of their peers who are otherwise developing typically.8-11 Yoshinaga-Itano et al. reported that early-identified children with cognitive impairments outperformed late-identified deaf children without cognitive impairments.12 Thus, the principles of early detection of hearing loss and early intervention are just as applicable in the child with multiple disabilities. With the advent of universal newborn hearing screening, the diagnosis of hearing impairment will in some cases precede that of cognitive impairment/developmental delay. In other words, the cognitive impairment may not be discovered until after cochlear implantation when language acquisition is seen to be delayed. In an effort to better predict cochlear implant outcomes in children with multiple disabilities, our group analyzed pre-implant functional disabilities and post-operative speech perception scores in 66 children with at least one disability in addition to their hearing loss.13 We asked if the functional disabilities identified in children prior to cochlear implantation could predict post-implant outcome. To answer this question, we devised a Functional Disability Score by modifying the Battelle Developmental Inventory Screening Test.14 The children in the study were scored by their audiologist (with information from their speech and auditory verbal therapists) in each of eight domains. The more cognitively influenced domains included Cognition, Receptive Language, Expressive Language, Personal-Social and Articulation. We also assessed Gross Motor Skills, Fine Motor Skills, and Receptive Vision. We scored the skills in each domain on a scale from 1 (severe delay) to 4 (age-appropriate skills) for a maximum developmental score of 32. We then created the Pediatric Ranked Order Speech Perception (PROSPER) score to evaluate speech perception outcomes in these children.13 This score was needed because assessments of speech perception after cochlear implantation in this group required several different tests. The PROSPER score allowed us to place the individual speech perception tests in a hierarchical order providing one score that could be used to follow progress over time (see Table 1). It was based on the progression of simple sound detection through pattern perception, closed-set, and open-set word recognition, described by Geers and Moog.15TABLE 1: Pediatric ranked order speech perception score.Importantly, we found a significant relationship between the pre-implant Functional Disability Score and post-implant PROSPER score, even after adjustment for age, age at activation, and duration of implant use. More specifically, the Functional Disability Score significantly predicted high (k>24) and low (k<7) PROSPER scores of post-implant speech perception. We have suggested that this information is useful in counseling parents regarding implantation because there may be children for whom these devices provide minimal benefit or perhaps have a disruptive influence on other areas of development. CONCLUSIONS AND TAKE HOME MESSAGE Cochlear implantation may provide significant benefits for children with cognitive delay. However, the risks associated with this patient group must be weighed against expected benefits. We suggest that, for children who are unable to provide reliable behavioral responses, the risks of providing uncomfortable stimulation through the cochlear implant or for missing device malfunctions may be too great to be justified by the potential benefits. The clinician must carefully consider the prospective benefits for each child, knowing that increasing functional disability (including cognitive domains) is associated with worsening post-implant speech-perception scores.