Long-Term Asymmetric Hearing Affects Cochlear Implantation Outcomes Differently in Adults with Pre- and Postlingual Hearing Loss

RESEARCH ARTICLE Long-Term Asymmetric Hearing Affects Cochlear Implantation Outcomes Differently in Adults with Pre- and Postlingual Hearing Loss Isabelle Boisvert1,2,3,7*, Catherine M. McMahon1,2, Richard C. Dowell2,4,5, Björn Lyxell6,7 1 Department Linguistics, Macquarie University, Sydney, New South Wales, Australia, 2 HEARing Cooperative Research Centre, Melbourne, Victoria, Australia, 3 SCIC Cochlear Implant Program - An RIDBC service, Sydney, New South Wales, Australia, 4 Department of Audiology and Speech Pathology, The University of Melbourne, Melbourne, Victoria, Australia, 5 Audiology, Royal Victorian Eye and Ear Hospital, Melbourne, Victoria, Australia, 6 Department of Behavioural Sciences and Learning, Linköping University, Linköping, Sweden, 7 Linnaeus Centre HEAD, The Swedish Institute for Disability Research, Linköping, Sweden * OPEN ACCESS Citation: Boisvert I, McMahon CM, Dowell RC, Lyxell B (2015) Long-Term Asymmetric Hearing Affects Cochlear Implantation Outcomes Differently in Adults with Pre- and Postlingual Hearing Loss. PLoS ONE 10(6): e0129167. doi:10.1371/journal.pone.0129167 Academic Editor: Johan J Bolhuis, Utrecht University, NETHERLANDS Received: December 14, 2014 Accepted: May 5, 2015 Published: June 4, 2015 Copyright: © 2015 Boisvert et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. Funding: This work was funded by the Macquarie University Research Excellence Scheme (http://mq. edu.au/) (IB), the HEARing CRC, established and supported under the Cooperative Research Centres Program – Business Australia (http://www.hearingcrc. org) (IB RD CM) and the Linnaeus Centre HEAD, The Swedish Institute for Disability Research (https:// www.liu.se/ihv/linnecentrum-head?l = en) (BL, IB). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Abstract In many countries, a single cochlear implant is offered as a treatment for a bilateral hearing loss. In cases where there is asymmetry in the amount of sound deprivation between the ears, there is a dilemma in choosing which ear should be implanted. In many clinics, the choice of ear has been guided by an assumption that the reorganisation of the auditory pathways caused by longer duration of deafness in one ear is associated with poorer implantation outcomes for that ear. This assumption, however, is mainly derived from studies of early childhood deafness. This study compared outcomes following implantation of the better or poorer ear in cases of long-term hearing asymmetries. Audiological records of 146 adults with bilateral hearing loss using a single hearing aid were reviewed. The unaided ear had 15 to 72 years of unaided severe to profound hearing loss before unilateral cochlear implantation. 98 received the implant in their long-term sound-deprived ear. A multiple regression analysis was conducted to assess the relative contribution of potential predictors to speech recognition performance after implantation. Duration of bilateral significant hearing loss and the presence of a prelingual hearing loss explained the majority of variance in speech recognition performance following cochlear implantation. For participants with postlingual hearing loss, similar outcomes were obtained by implanting either ear. With prelingual hearing loss, poorer outcomes were obtained when implanting the long-term sounddeprived ear, but the duration of the sound deprivation in the implanted ear did not reliably predict outcomes. Contrary to an apparent clinical consensus, duration of sound deprivation in one ear has limited value in predicting speech recognition outcomes of cochlear implantation in that ear. Outcomes of cochlear implantation are more closely related to the period of time for which the brain is deprived of auditory stimulation from both ears. PLOS ONE | DOI:10.1371/journal.pone.0129167 June 4, 2015 1 / 11 Cochlear Implantation and Long-Term Hearing Asymmetry Competing Interests: The authors have declared that no competing interests exist. Introduction Cochlear implants have been dubbed ''the most successful of all neural prostheses'' [1], helping to partly restore hearing in more than 300 000 people around the world [2]. For most adults receiving a cochlear implant, only one ear is implanted despite a bilateral hearing loss. It is therefore desirable to choose the ear for implantation that optimises communication outcomes. The criteria for implantation are broadening and individuals with more residual hearing are being offered a cochlear implant as a solution to their communication difficulties. There is, however, a relative lack of evidence to guide clinicians in choosing the best ear for implantation. This is particularly the case for adult patients with asymmetric hearing thresholds or different durations of sound deprivation in each ear where they perceive one ear to be “better” and the other “poorer”. In these situations, clinicians and patients face the dilemma of either choosing to implant the poorer ear, where the outcomes are unknown, or risk implanting the better ear where residual hearing may be lost. Therefore this study specifically aimed to examine the effects of unilateral sound deprivation on cochlear implantation outcomes in patients with bilateral hearing loss. Duration of deafness is commonly identified as one of the main predictors of implantation success in adults, where higher performance in speech recognition is associated with shorter durations of deafness [3–5]. The association between long duration of deafness and poor implantation outcomes is also supported by literature using animal models of deafness showing the degradation of peripheral neural structures [6], such as the spiral ganglion cells [7,8] and the cochlear nucleus [9]. These studies have been used to support the assumption that in humans, the longer an ear has been deprived of hearing the more limited the outcomes with the cochlear implant will be for that ear. This assumption, however, is largely derived from studies in which most participants had similar hearing thresholds and/or auditory stimulation in both ears [3,10,11], or in which a hearing aid (i.e. not a cochlear implant) was reintroduced after a period of sound deprivation [12]. This assumption is further reinforced by studies investigating outcomes of cochlear implantation and hearing asymmetries in early childhood deafness [13,14]. Conversely, in adults, better hearing in one ear could contribute to higher outcomes of implantation in the other ear [15]. This idea is derived from the suggestion that hearing in one ear may contribute to the preservation of: 1) peripheral neuronal struc (...truncated)