Determinants of auditory performance after cochlear implantation in post-lingual adults: beyond the duration of hearing loss.

PURPOSE: Prolonged auditory deprivation progressively compromises central auditory pathway integrity, yet its prognostic impact in post-lingual adults undergoing cochlear implantation remains poorly defined. This study evaluates the influence of hearing loss duration - expressed in absolute terms, dichotomised by the conventional 10-year threshold, and as a proportion of lifetime with hearing loss - on auditory performance, and identifies the clinical determinants associated with the immediate activation effect and the post-implantation trajectory.

METHODS

Single-centre, retrospective, observational study at Unidade Local de Saúde de Santo António, including 109 post-lingual adults undergoing CI between 2018 and 2024, with a minimum follow-up of 12 months. Auditory performance was assessed through pure-tone average, speech reception threshold, and speech discrimination score. Longitudinal modelling used linear mixed-effects models, distinguishing the immediate activation effect from subsequent temporal progression.

RESULTS

Patients with longer hearing loss duration presented greater pre-implantation auditory impairment across all metrics, following a continuous dose-response relationship with no evidence of a threshold effect. The 10-year criterion showed no discriminative value - either in the immediate effect or in the post-implantation trajectory, which was equivalent between groups. Ear selection for implantation and pre-operative hearing aid status were the strongest determinants of the level reached at activation. The proportion of hearing loss duration covered by hearing aid use was the only predictor associated with superior longitudinal recovery in the speech metrics.

CONCLUSION

In this cohort, duration of hearing loss did not identify patients who failed to benefit, and these single-centre data do not support its use as a stand-alone exclusion criterion for cochlear implantation. For most determinants, the functional differential established at activation was maintained throughout follow-up without compensatory catch-up, making optimisation of the level reached at activation the principal target of intervention. Individualised consideration of the ear to be implanted, maintenance of hearing aid use until the date of surgery, and maximisation of the proportion of hearing loss duration covered by hearing aid use constitute the main modifiable targets for intervention, and are associated with functional outcomes.