Longitudinal Cochlear Implant Outcomes in Danish Adults: Changes in Speech Recognition, Self-Reported Hearing Ability, Hearing-Related Quality of Life, and Tinnitus

<b>Background:</b> This study assessed the efficacy and effectiveness of cochlear implants (CIs) by examining changes in speech recognition, self-reported hearing ability, hearing-related quality of life, and tinnitus over two years. <b>Methods:</b> A prospective two-year longitudinal study included 50 adult users of CI. Speech recognition in quiet and background noise was measured using Dantale I (with/without visual cues; fixed 0 dB SNR) and the adaptive Hearing in Noise Test (HINT). Self-reported outcomes were obtained using the Speech, Spatial, and Qualities of Hearing Scale (SSQ-12), Nijmegen Cochlear Implant Questionnaire (NCIQ), and Tinnitus Handicap Inventory (THI). <b>Results:</b> In post-lingually deafened users of CI (N=46), Dantale with visual cues improved from 74.2% to 94.9% (mean difference = 20.7% [95% CI: 15.8, 25.6], p<0.001, dz=1.83), and without visual cues from 58.9% to 92.1% (33.1% [28.0, 38.2], p<0.001, dz=2.83). Dantale with background noise improved from 23.4% to 61.7% (37.6% [32.4, 42.8], p<0.001, dz=3.13), and adaptive HINT from 8.6 to 4.2 dB SNR (-5.8 [-7.0, -4.6], p<0.001, dz=3.10). NCIQ scores increased from 292.6 to 436.3 points (145.3 [122.8, 167.8], p<0.001, dz=3.11), and SSQ-12 improved by 0.60 points [0.18, 1.02] from 1 to 2 years (p=0.015, dz=0.86). Tinnitus severity remained low at the group level, with individual fluctuations over time. <b>Conclusions:</b> Danish adult users of CI showed substantial and sustained improvements in speech recognition and hearing-related quality of life over two years, with adaptive speech-in-noise testing proving particularly sensitive for detecting long-term changes.