Additional health-related quality of life
The disease-specific quality of life measured by the NCIQ improved significantly after the first CI and again after the second CI. The mean total NCIQ score before any CI was 42.80 ± 17.84. After a first CI, it improved to 55.66 ± 16.06 (p < 0.000) and then improved further to 63.28 ± 18.53 (p = 0.012) following the second CI (see Fig. 1a). NCIQ subdomains, including basic sound perception, advanced sound perception, speech production, self-esteem, and social interactions, significantly improved after both CIs, except for subdomain NCIQ 3, i.e. speech production (see Table 1).
Audiological improvement—unilateral versus bilateral CI
The mean value FB MS for the first implanted ears was 6.05 ± 11.85; on contralateral ears, it was 10.87 ± 16.42. After first CI, FB MS increased to 48.69 ± 28.94 (p < 0.001). After the second CI, the FB MS improved further to 66.43 ± 19.57 (p = 0.002) with bilaterally active CI. After the second CI operation, both ears were also investigated with only one active CI. The second operated ear performed slightly better 56.59 ± 19.24 versus the first operated ear 50.68 ± 22.16. However, the difference was not statistically significant.
When speech and noise were presented from the front, the mean OLSA SNR was 0.368 ± 3.109 dB SPL with a bilateral CI, while the mean OLSA SNR was 1.881 ± 4.459 dB SPL with a unilateral CI. The 1.513 dB SPL difference was significant (p = 0.002). If the speech was presented to the first implanted ear, and noise to the deaf ear, the mean OLSA SNR was − 4.241 ± 5.338 dB respective to the contralateral CI − 3.518 ± 5.00 dB SPL. The difference, in this case, was not significant (p = 0.115). Speech understanding measures were justifiably the lowest observed when noise was presented to the CI ear and speech to the deaf ear at 7.231 ± 4.65 dB SPL in unilaterally implanted patients.
Subjective hearing ability
The first CI resulted in a significant improvement in the mean total OI score. Before a first CI, the mean total OI score was 1.81 ± 0.55, but this improved to 3.22 ± 0.55 after the first CI. All three subdomains, "OI quiet", "OI noise interference", and "OI directional listening", significantly improved, and further progress after a second CI was observed in all OI subdomains.
In the study cohort, tinnitus annoyance was reduced by the first CI to a low level and declined even further after secondary surgery. Twenty-one patients (72%) reported tinnitus of some kind before CI implantation, with a mean total TQ score of 27.52 ± 19.67. TQ decreased after the first CI to 15.68 ± 20.37 (p = 0.004) and decreased further after the second to 11.00 ± 13.44 (p = 0.041). Before any CI, five patients (23.8%) reported decompensated tinnitus (total TQ score > 46). After the first CI, two patients in the decompensated tinnitus subgroup achieved intermediate levels (total TQ score 31–46). One patient reported a complete absence of tinnitus, and two reported continuous high tinnitus annoyance. These two patients profited from the second CI, with one achieving low-level and the other intermediate-level tinnitus. Each of the three patients (14%) with intermediate tinnitus annoyance before the first CI reported a decrease to low tinnitus levels (total TQ score 0–30) after the procedure, and this reduction persisted after the second CI. All subscales scores, including emotional and cognitive distress, intrusiveness, auditory perceptual difficulties, sleeping disturbances, but somatic complaints, declined significantly after the first CI and again after the second CI (see Table 1).
To measure the psychosocial burden of CI patients, PSQ, COPE, GAD 7, and ADS questionnaires were filled by the patients and analysed by qualified staff. The perceived stress questionnaire showed relatively low levels of preoperative stress, with a mean total PSQ of 0.31 ± 0.17. PSQ total scores remained stable over time. Only the PSQ subscale demands demonstrated a significant reduction after the first CI (p = 0.037), and this value remained stable after the second procedure (see Fig. 1d), thereby implying that neither surgery increased patients' stress.
The COPE questionnaire has four subdomains, namely avoidance, seeking support, positive thinking, and active problem-solving. COPE scores have not changed significantly after the first CI. However, significant reductions in three of the four subdomains (avoidance, seeking support, and positive thinking) were observed after the second implantation (see Table 1). That may be because coping and problem-solving strategies are less essential after a second CI, thus removing some of the limitations of monaural hearing.
The mean score of the ADS depression questionnaire was 13.28 ± 8.84 before any CI, and 10 of the 29 (34.4%) patients scored 16 or more, which is a degree of depression that is understood to be deserving clinical treatment. There was a slight reduction after the first CI, and a very slight increase after second CI. However, these changes were not significant (p = 0.546 and p = 0.862).
The mean of the GAD-7 questionnaire, which assesses fear, was 3.75 ± 4.56 pre-CI, which indicates minimal to mild anxiety. After the first CI, the mean GAD-7 declined to 3.29 ± 3.94 (p = 0.049). After the second CI, it was 4.10 ± 3.90 (p = 0.807). Before CI, nine of the 29 (31%) patients reported at least mild anxiety (4–9 pt.) , and this has not changed after either CI.
Correlation of health-related quality of life, psychosocial burden, and hearing
Pearson correlations were performed in order to gain a better understanding of the relations between HRQoL (NCIQ), tinnitus distress (TQ), stress (PSQ), generalised anxiety disorder (GAD-7), depression (ADS), coping (COPE), subjective quality of hearing (OI), and hearing performance with background noise. The heat maps summarise the correlations after the first and after the second CI (see Fig. 2). For the sake of clarity, we used two mean total scores for NCIQ, TQ, PSQ, GAD-7, and ADS, namely the COPE subscale "seeking support" and the signal-to-noise ratio presented from the front. The first main finding is that after the first CI, tinnitus distress correlated significantly with subjective hearing ability and speech recognition, and after the second CI, tinnitus distress significantly decreased and the previous correlation disappeared. The second main finding is that the correlation between HRQoL and subjective hearing ability is quite strong (Pearson correlation coefficient = 0.543) and becomes even more significant after the second CI (Pearson correlation coefficient = 0.917), highlighting the importance of sufficient hearing capacity for a good quality of life.