This topic has garnered so much attention that there are scientific and clinical conferences dedicating entire sessions to CI for SSD. In fact, there is even a multi-national working group tasked with developing a uniform assessment protocol for this population (Audiol Neurootol. 2016;21:391). As is often common with emerging or hot topics in any field, there is considerable disagreement among professionals if this is a viable intervention for adults and/or children with SSD. Much of the controversy stems from the fact that CI for SSD is not an approved indication by the Food and Drug Administration (FDA), so all data have resulted from outside the United States, or from off-label implantations within the country. A systematic review of the SSD-CI literature published in 2015 concluded that all published works on this topic include “non-randomized, low or moderate level of evidence” (Otol Neurotol. 2015;36:209). Thus, there is a need for prospective, controlled studies with larger sample sizes.
While we wait for the results of more controlled studies, why would we even consider cochlear implantation for individuals with SSD? One might be particularly concerned about implantation for children with SSD considering research evidence that shows how single-sided hearing is sufficient for a child to develop speech and language within the normative age range. However, children with SSD have exhibited significantly greater fatigue, stress, and increased academic risk compared with their normal-hearing peers (e.g., Scand Audiol Suppl. 1988;30:71; Ear Hear. 1998;19:339; Trends in Amplification. 2008;12:7; Pediatrics. 2010;125 e1348; B-ENT. 2013;Suppl 21:107). In addition, a single-hearing ear affords little-to-no spatial awareness of sound (e.g., Otol Neurotol. 2011;32:39; Otol Neurotol. 2015;36:209; Audiol Neurotol. 2016;21:127; Ear Hear. 2017;38:611), which is a safety concern, particularly for children who might not be consciously aware of this deficit. For adults with acquired SSD, there are multiple reports of cochlear implantation resulting in significantly improved quality of life (Laryngoscope. 2017;127:1683; Clin Otolaryngol. 2016;41:511; Otorhinolaryngol Relat Spec. 2015;77:339), tinnitus suppression (Ann Otol Rhinol Laryngol. 2008;117:645; Audiol Neurotol. 2015;20 Suppl 1:21; Hear Res. 2013;295:24; Acta Otolaryngol. 2016;13:460; Am J Otolaryngol. 2017;38:226), significantly improved localization abilities (e.g., Otol Neurotol. 2011;32:39; Otol Neurotol. 2012;33:1339; Otol Neurotol. 2013;34:1681; Otol Neurotol. 2014;35:1525; Otol Neurotol. 2015;36:1467; Otol Neurotol. 2016;37:e154; Otol Neurotol. 2016;37:e332), and improved speech recognition with noise directed at the better hearing ear (e.g., Otol Neurotol 2011;32:39; Otol Neurotol. 2012;33:1339; Otol Neurotol. 2015;36:1467; Clin Otolaryngol. 2016;41:511).
Though there are data supporting CI as a viable and highly-effective treatment option for individuals with SSD, these recent peer-reviewed articles add relevant updates to consider in clinical practice.
CI WEAR TIME OF CHILDREN WITH SSD
One of the most basic markers of the success of an auditory intervention (i.e., hearing aid, CI, or bone-anchored implant) is whether the patient uses the device. Though this may seem like an overly simplistic measure, there are CI recipients who ultimately become non-users of their devices (e.g., Cochlear Implants Int. 2000;1:18; Otorhinolaryngol. 2013;77:407; Cochlear Implants Int. 2015;16:186). Non-users, while relatively few, tend to be those implanted late in adolescence with longer experience of deafness (> 20-30 years) and/or who communicate primarily via sign language. Many professionals fear that children with SSD are at risk of becoming non-users given their normal hearing in the contralateral ear. Thus, Polonenko and colleagues aimed to quantify CI wear time of the seven pediatric CI recipients (mean age at CI = 5.9 years; range 1.1 to 14.1 years) with SSD who received implants and followed by The Hospital for Sick Children in Toronto, Ontario at the time of study completion (Ear Hear. 2017;38:681). Five of the seven children had congenital deafness, and the remaining two had acquired deafness in adolescence. Using the data-logging feature of the CI software, they quantified the mean duration of use (hours/day) as well as the frequency and duration of “coil-off” episodes. The mean duration of CI experience at the time of data log analysis was 5.2, months with a range of 1.3 to 22.5 months.
Polonenko and colleagues found that the children wore their CI processor for 7.4 hours per day on average, with a range of 3.5 to 11.4 daily hours (Ear Hear. 2017;38:681). They also found that there was a significant relationship between the recipient age and the hours of daily CI usage. The number of coil-off episodes was quite variable with a range of 5.4 to 36.4 times per day (mean = 22.0), with the greatest number of episodes for the youngest children, as expected. They also found that the number of coil-off episodes significantly decreased with CI experience.
These data suggest that (1) children with SSD who received a CI wear the processor for a significant portion of each day; (2) older children wore their processors for longer daily durations compared with younger children; and (3) the number of coil-off episodes significantly decreased with CI experience. These studies provide the first snapshot of CI device usage among SSD and near-SSD recipients, suggesting a favorable outcome as children do, in fact, wear their CIs throughout the day.
SPEECH RECOGNITION WITH CI
Greaver and colleagues presented case study data for five children with either true SSD (n = 1) or near-SSD (n = 4) hearing configurations (Am J Audiol. 2017;26:91). The children in this study were implanted at 5.3 years old on average, with a range 2.3 to 8.7 years old. Two of the five children had congenital deafness, two had acquired hearing loss, and the final recipient's age at onset was unknown. All children demonstrated expressive and receptive language within the age normative range prior to implantation, which is not unexpected. Baseline speech recognition scores in the poorer hearing ear were attempted but were unattainable due to the extremely poor audiometric detection thresholds and unreliable speech detection even at suprathreshold levels.
Three to 12 months of CI wear time data were obtained. Greaver and colleagues found that the children with SSD use CIs around 7.8 hours a day, with a range of 3.7 to 11.9 hours—results that were quite similar to those reported by Polonenko, et al. (Am J Audiol. 2017;26:91). The group also reported postoperative speech recognition data for the implanted ear using direct audio input of recorded materials via Roger or Bluetooth connection. Monosyllabic word recognition (PBK or CNC) was administered on four of the five children with postoperative CI-only scores that range from 52 to 80 percent (mean = 66%). The fifth child (S5) was only at three months post-activation at the time of manuscript preparation and got 100 percent ESP words, 88 percent ESP spondees, 79 percent ESP monosyllables, and eight percent correct for recorded MLNT words. All children demonstrated highly significant speech recognition improvement in the CI ear and wear their CIs up to all-waking hours—both indicative of a successful intervention.
PRE- AND POST-IMPLANT STUDY
This last study reported pre- and post-implant data for a child who acquired SSD at 5 years of age and got a CI a year later (Otol Neurotol. 2016;37:e26). The authors obtained cortical auditory evoked potentials (CAEPs), cortical visual evoked potentials (CVEPs), and cortical somatosensory evoked potentials (CSSEPs) at various time points pre- and post-implantation. All evoked potentials were measured using a 128-channel net placed on the patient's scalp for high-density electroencelography (EEG), similar to that shown in the figure (Front Neurol. 2012;3:77). High-density EEG allows researchers to measure electrical potentials across multiple sites and to derive spatial estimates of the underlying cortical sources responsible for the potentials. In the current study, the use of high-density EEG with multiple sensory evoked potentials across various time points allowed for a description of the effect of unilateral deafness (re: age normative sample) and the change in cortical activation patterns following cochlear implantation.
Sharma and colleagues reported that with auditory speech stimuli presented to the poorer hearing ear prior to implantation, there was a significantly delayed P1 response with abnormal morphology (N1 and P2 both absent), and primarily ipsilateral activation of temporal (A1) and frontal areas (Otol Neurotol. 2016;37:e26). This result indicated a highly abnormal response with respect to both the routing of activation (ipsilateral vs. contralateral hemisphere) and the breadth of activation (frontal and temporal areas vs. temporal only). Frontal activation, particularly of the inferior and superior frontal gyrus, is linked with increased auditory attention; thus, this result is not surprising given that presentation of sound to the poorer hearing ear would require greater auditory attention. This child was re-tested at three to 14 months post-CI activation. Sometime between three and eight months post-activation, there was a significant change in CAEP morphology such that both N1 and P2 (re)appeared as well as a significant decrease of P1 latency. These changes reflect neuroplasticity or auditory cortical reorganization following cochlear implantation in a child with SSD.
A secondary but highly substantial finding in this study was that at the preoperative time point, non-auditory stimulation (vision and touch) resulted in significant activation of the auditory cortex—even greater than the activation of the visual cortex in response to visual stimulation. This finding provided evidence for cross-modal plasticity following post-lingual acquisition of SSD. Postoperatively, however, with 27 months of CI experience, auditory cortical activation in response to non-auditory stimulation was significantly reduced (i.e., improved) with a clear redistribution of activation closer to the primary sensory cortices for vision (occipital lobe) and touch (parietal lobe). Thus, this study demonstrated abnormal auditory and cross-modal plasticity in response to acquired, unilateral deafness and, more importantly, a reversal of this maladaptive plasticity following cochlear implantation.
There is a growing body of evidence supporting the efficacy of cochlear implantation for children and adults with SSD; however, in the absence of FDA approval for SSD, each case must be approached individually, particularly for insurance coverage that often requires multiple appeals and peer reviews. Some clinicians and researchers advocate for the use of alternative treatment options such as CROS hearing aid systems, remote microphone systems, and bone anchored implants. These interventions hold face validity as they can offer a successful rehabilitative option that is less invasive than cochlear implantation (e.g., Otol Neurotol. 2012;33:291; Otol Neurotol. 2017;38:11; Otolaryngol Head Neck Surg. 2017;157:565). However, none of these interventions can provide a binaural representation of incoming auditory stimuli. As such, these options are incapable of reversing the effects of asymmetric auditory neural development and the maladaptive cross-modal reorganization of the central auditory system (e.g., Brain. 2013;136:160; Neurotology. 2015;20[Suppl 1];13; Otol Neurotol. 2016;37:e26). In contrast, a CI is currently the only possible intervention capable of providing the recipient with bilateral auditory input with the possibility of binaural hearing (e.g., Audiol Neurootol. 2015;20:183; Audiol Neurotol. 2016;21:127).
For adults with acquired SSD and children with SSD whose parents have expressed interest in obtaining a CI in the poorer hearing ear, cochlear implantation is a viable intervention that can significantly improve auditory neural development, speech understanding in the poorer ear, speech understanding in noise, spatial hearing abilities, and overall quality of life.
Copyright © 2017 Wolters Kluwer Health, Inc. All rights reserved.