Role of cochlear reserve in adults with cochlear implants following post-lingual hearing loss

Introduction Pre-operative assessments before cochlear implantation (CI) includes the examination of both tone hearing, and the level of the cochlear reserve indicated by speech understanding. The goal of this study was to explore the predictive influence of tone hearing and cochlear reserve in CI. Methods We did a retrospective cohort study, which included adult patients who had undergone CI between January 2012 and December 2019 in a tertiary care center. The pre-operative tone hearing, unaided maximum monosyllabic word recognition score (WRSmax), aided hearing gain, aided monosyllabic word recognition score at 65 dB (WRS65(HA)), and speech perception gap (SPG) were measured. The duration of unaided hearing loss (UHL) was also assessed. These variables were compared with post-operative monosyllabic word recognition score after CI at 65 dB (WRS65(CI)). Results 103 patients and 128 ears were included in this study. Regardless of tone hearing, patients with better pre-operative WRSmax and WRS65(HA) performed better post-operatively. WRSmax was found to be the most important factor that was statistically significantly associated with WRS65(CI). SPG was statistically significantly associated with WRSmax and SPG >= 20% group performed better post-operatively. Any duration of unaided hearing loss was statistically significantly inversely associated with WRSmax above 0%. Conclusion Cochlear reserve represented by WRSmax may play the most important role as a predictive factor in outcomes after CI. SPG should be considered for indicating CI in patients, when WRS65(HA) does not reach WRSmax. Early rehabilitation with hearing aids and duration of hearing aid usage might play an important role in preserving cochlear reserve in adults.