3.1. Patient Collective
The 136 adult tinnitus patients (56 ♀, 80 ♂) included in this study had a mean age of 50.9 ± 15.5 a. Female (51.3 ± 15.5 a) and male patients (50.6 ± 15.5 a) did not differ significantly in their mean age (Student’s t-test, p=0.79). The adult patient collective was divided into three age categories of young (<39 a; n=18; mean age (± standard deviation): 23.9 ± 3.6 a), middle aged (40 – 59 a; n=85; 48.8 ± 7.6 a) and senior (60+ a; n=33; 70.6 ± 7,6 a) patients to account for age related hearing changes and comorbidity burden. The patients reported either monaural (young: n=13; middle aged: n=38; senior: n=19) or binaural (young: n=5; middle aged: n=46; senior: n=13) pure tone (young: n=12; middle aged: n=56; senior: n=21) or narrowband noise tinnitus (young: n=6; middle aged: n=28; senior: n=11). Usually, only one kind of tinnitus percept with a determinable center frequency was reported, even though in the case of a binaural percept the frequency could differ; only two patients (one middle aged and one senior) reported pure tone in one ear and narrowband noise in the other. Only the audiograms of the patients’ tinnitus-affected ears were used for the analyses described below, so different center frequencies of both ears did not affect the evaluation. The patients’ TF in the three age groups was not significantly different from each other (median frequency (interquartile range)): young: 4000 Hz (750 Hz, 8000 Hz); middle aged: 4000 Hz (2000 Hz, 6000 Hz); senior: 4000 Hz (1000 Hz, 6000 Hz); Kruskal-Wallis ANOVA: H(2, 202)=2.30, p=0.32. The same was true for the tinnitus loudness, given in dB sensation level (dB SL) (young: 7 dB SL (0 dB SL, 10 dB SL); middle aged: 7.5 dB SL (-3 dB SL, 15 dB SL); senior: 10 dB HL (2 dB SL, 19 dB SL); Kruskal-Wallis ANOVA: H (2, 196)=2.97, p=0.23). Nevertheless, patients in the three age categories showed a significant different number (Χ² (20,136)=13.58, p=0.035) of non-auditory comorbidities (cf. Methods), these are summarized in Table 2. Trivially, with increasing age the number of non-auditory comorbidities rises significantly (Kruskal-Wallis ANOVA, H(3, 136)=14.93, p<0.001) and Multiple Comparison of means post-hoc tests show that young patients show significantly less non-auditory comorbidities than middle aged (p=0.015) or senior patients (p<0.001), while those two last groups did not show significant differences in comorbidity numbers (p=0.25). When analyzing the tinnitus frequency with these non-auditory comorbidity categories in the three age groups independently, we also did not see any significant differences between the median frequency of patients with different numbers of comorbidities (young: Mann-Whitney U-test, p=0.21; middle aged: Kruskal-Wallis ANOVA, H (3, 132)=6.12, p=0.11; senior: Kruskal-Wallis ANOVA, H (3, 47)=0.94, p=0.82). This is also true for the tinnitus loudness (young: Mann-Whitney U-test, p=0.48; middle aged: Kruskal-Wallis ANOVA, H (3, 128) = 3.70, p=0.30; senior: Kruskal-Wallis ANOVA, H (3, 46)=3.54, p=0.32). In other words, neither tinnitus frequency nor tinnitus loudness did show any dependency on the patient’s age.
Those 45 (33 %) tinnitus patients without any non-auditory comorbidities were seen as “standard tinnitus patients” to which the other comorbidity groups could be compared. In the young patients group, only data of patients with one non-auditory comorbidity could be compared to them. In the two other age groups, we could compare the data of patients with one to five non-auditory comorbidities to these “standard tinnitus patients”.
3.2. Correlation of the Audiometric Data of Tinnitus Patients with and without the Presence of Non-Auditory Comorbidities
In first analyses, the pure tone air-conductance audiometric HL of the patients of the three age groups was assessed independently by two-factorial ANOVAs with the factors
frequency and
number of non-auditory comorbidities. As mentioned above, for the young patients group, only the comparison between zero and one comorbidity was possible. The results are summarized in
Figure 1. In all patient groups we found a significant effect of the HL on
frequency (not shown in Figure; young: F (10, 374)=1.92, p=0.041; middle aged: F (10, 1826)=59.49, p<0.001; senior: F (10, 672)=35.90, p<0.001). We also found a dependency of the HL on the
number of non-auditory comorbidities. In the young tinnitus patients, the mean HL was significant weaker with one of these comorbidities (
Figure 1A, inset; F (1, 374)=10.61, p=0.001), while the middle aged tinnitus patients did show a significantly increased HL with one non-auditory comorbidity (
Figure 1B, inset; F (3, 1826)=5.05, p=0.002). Senior tinnitus patients showed a significant increased HL only with three or more non-auditory comorbidities (
Figure 1C, inset; F (3, 672)=2.87, p=0.036). No interaction of the two factors could be found in the three age groups (
Figure 1 A to C; young: F (10, 374)=0.22, p=0.99; middle aged: F (10, 1826)=0.69, p=0.90; senior: F (10, 672)=0.39, p=0.99). In other words, dependent on the tinnitus patients’ age and number of non-auditory comorbidities, the hearing thresholds can be significantly different, even if no further auditory comorbidities are present. Note, that only in the senior tinnitus patients we find a steadily increasing mean HL with increasing number of comorbidities while in the middle aged patients this dependency is non-linear and in young patients even inverted.
It is well known that the maximum of the HL and the TF correlate with each other. Usually the TF is found to be at the frequency of the maximum HL but comorbidities and / or age might have an influence on this correlation. Therefore, we analyzed the HL dependent on the
distance of the tested frequency to the determined tinnitus frequency (TF) given in octaves and the
number of non-auditory comorbidities with independent ANOVAs for each age group. For better comparison, we used only the distance range of -4 to +2 oct relative to the TF, which includes 81.5% (1812/2222 data points) of the complete HL data provided above. The reasoning behind these analyses was to investigate if the HL – as mentioned above – is dependent on the distance to the TF and if this dependency is further dependent on the
number of non-auditory comorbidities. We found, first, in young tinnitus patients the expected dependency of the HL on the distance to TF (
Figure 1D, inset; F (6, 179)=3.46, p=0.003) with the maximum HL at +1 oct relative to the TF (Tukey post-hoc tests, p<0.05). No difference between HL without any non-auditory comorbidities and one comorbidity was found (not shown in Figure; F (1, 179)=0.002, p=0.97) and no significant interaction was found (
Figure 1D; F (6, 179)=1.74, p=0.11). Second, in the middle aged tinnitus patients again the expected dependency of HL and distance to TF was found (
Figure 1E, inset; F (6, 1174)=29.24, p<0.001) with the maximum HL at the TF (Tukey post-hoc tests, p<0.001). No difference in mean HL between the number of non-auditory comorbidities was found (not shown in Figure; F (3, 1174)=0.38, p=0.77) but we found a significant interaction of both factors (
Figure 1E; F (18, 1174)=2.42, p<0.001). Tukey post-hoc tests indicated that especially the HL of the tinnitus patients without any non-auditory comorbidities showed a different peak-TF location compared to the other comorbidity groups (p<0.05). Finally, in the senior age group we found a sigmoidal shaped dependency of the HL on the distance to the TF (
Figure 1F, inset; F (6, 385)=15.10, p<0.001) with a maximum at the maximum of the investigated range of +2 oct relative to TF (Tukey post-hoc tests, p<0.001). We also found a significant dependency on the number of non-auditory comorbidities (not shown in Figure; F (3, 385)=7.63, p<0.001) with the “3+” category having significantly higher HL values compared to two of the other three categories (Tukey post-hoc tests, “0 vs. 3+” and “2 vs. 3+”, p<0.05; “1 vs. 3+”, p=0.075). The interaction of both factors did show a significant value as well (
Figure 1F; F (18, 385)=3.48, p<0.001). Here the peak of the HL was at the TF for one and two non-auditory comorbidities, while for the two extreme cases (“0” and “3+”) the maximum HL was found at +2 oct relative to the TF (Tukey post-hoc tests, p<0.001). In other words, the statement that the maximum HL can be found at or around the TF is only partially true and dependent on the factor age and more importantly also on the number of non-auditory comorbidities. Again, no “simple” linear correlation of the data with the number of non-auditory comorbidities could be identified.
With this knowledge, we aimed to identify the possible non-auditory comorbidity (or comorbidities) that affected the HL in the different tinnitus patient age groups most. The non-auditory comorbidities were separated into seven categories (cf. Methods). The patients’ mean HL of the different age groups was then analyzed by independent two-factorial ANOVAs with the factors
frequency and
non-auditory comorbidity presence (i.e., with or without the specific comorbidity). The results of all analyses are given in
Table 3. Note that analyses were not possible in all age groups dependent on the specific non-auditory comorbidity; we refrained from using the data of the young patients completely (cf.
Table 1). From the analyses it became obvious that frequency dependent HL was mostly independent from the non-auditory comorbidity in middle aged and senior tinnitus patients, as in all cases the “standard” HL-pattern of low HL in lower frequencies and higher HL in higher frequencies was either significant or showed a tendency (column
frequency in
Table 3). The analyses of the factor comorbidity presence resulted in a more differentiated picture. In the case of diseases of the endocrine system / metabolism, patients of these two age groups with enough data for analysis showed significantly higher HL without that non-auditory comorbidity compared to patients with that specific comorbidity. In the remaining six categories of non-auditory comorbidities middle aged tinnitus patients showed higher HL with the specific comorbidity in two categories (digestive and muscle-skeletal system), senior patients showed this only with circulatory system comorbidities. Finally. We found interactions of both factors (i.e., frequency and presence of a comorbidity) only in one case, namely in middle aged tinnitus patients with or without muscle-skeletal system comorbidities. In other words, in all other cases with significant differences in mean HL dependent on the non-auditory comorbidity the whole audiogram was shifted in a parallel manner, which was not the case in this specific group.