RP201 - Pre-Surgery Hearing Threshold as a Predictor for Cochlear Implant Outcome

Abstract:
Cochlear implants should be considered for persons with severe to profound hearing loss. The decision must be well founded and improve everyday life. Predicting outcome of a cochlear implant is affected by several factors, where pre-surgery hearing thresholds is one. Our study shows a correlation between pre-surgery hearing threshold and post-surgery speech perception. The outcome is affected by the level and configuration of the hearing thresholds. If a person meets the CI candidacy criterion it seems plausible that surgery should be performed while the quality of hearing is as good as possible and before speech perception deteriorates further.

Summary:
Objectives
Cochlear implants should be considered for every person with severe to profound hearing loss (Turton et al, 2020). Prediction of outcome of cochlear implants (CI) in adults is of interest for CI candidates as well as professionals when deciding for surgery. The influence of pre-surgery hearing thresholds on outcome of CI for adults have had increasing focus during the 21th century (e.g. Lammers et al, 2018, Gratacap et al, 2016, Lee et al, 2021). However, previous studies show no consensus of the impact of pre-surgery hearing thresholds on post-surgery speech perception. Besides the pre-surgery hearing thresholds, the duration of severe-to-profound hearing loss and onset of hearing loss affects the outcome of CI (Bernhard et al, 2021). Furthermore, the etiology of hearing loss and previous sound stimulation affects the outcome (Blamey et al, 2013, Caposecco et al, 2012, Kang et al, 2016).

Aim
The present study aimed to evaluate post-surgery outcome for speech perception when configuration of pre-surgery hearing thresholds were considered.

Design
An experimental study at the Audiological research Centre in Örebro, Sweden, evaluated the outcome for 105 adult persons whom all went through CI surgery. Clinical data from pure tone audiogram and monosyllabic speech testing pre- and post-surgery were examined and statistical significance were sought.

According to pre-surgery hearing thresholds, the participants were divided in 4 groups. From better to worse hearing; sloping audiogram, steep sloping audiogram, corner audiogram and complete deafness. All participants hade pure tone average (PTA4) of 70 dB HL, which equals the criterion for CI candidacy in Sweden.

Results
As expected persons with better pre-surgery hearing thresholds had better post-surgery speech perception, i.e. persons with sloping audiograms. Between the four groups of audiograms the post-surgery average speech perception varied between 48% and 61%. The improvement in speech perception had no significant difference between the groups, on average the improvement were 25% with the largest improvement were seen for the group with steep sloping audiograms, 28% improvement. If the non-implanted ear were evaluated in comparison with the outcome it was evident that the speech perception not just relied on the implanted ear. The non-implanted ear had a strong impact on the result. If the non-implanted ear had an speech perception >40% there were significant better result post-surgery than for those who had speech perception < 40% in the non-implanted ear.

Conclusion
Pre-surgery hearing thresholds are of importance when predicting outcome of CI-surgery for speech perception. Also noticeable, is that both ears have an influence on the result and not just the implanted ear, and should be taken into consideration when predicting outcome of CI-surgery.