Abstract
BACKGROUND: The aim of this study was to evaluate the relationship between sound level tolerance and tinnitus in humans. METHODS: We compared the loudness discomfort levels at 500 and 3000 Hz pure tones in 33 subjects with bilateral tinnitus and 33 subjects with unilateral tinnitus with normal and symmetric hearing thresholds and those of age- and sex-matched control subjects. RESULTS: Both the tinnitus ears (108.18 ± 10.22 dB HL and 103.03 ± 11.04 dB HL) and non-tinnitus ears (108.94 ± 12.61 dB HL and 104.24 ± 11.60 dB HL) in the unilateral tinnitus subjects showed significantly lower loudness discomfort levels at 500 and 3000 Hz than the control ears (115.91 ± 6.78 dB HL and 111.52 ± 8.88 dB HL, P < .008; α=0.05/6=0.008), whereas there was no difference in the loudness discomfort levels of the tinnitus ears of the bilateral tinnitus subjects (111.52 ± 10.42 dB HL or 106.36 ± 11.34 dB HL) and the control ears. CONCLUSION: These results support the hypothesis that the reduced loudness discomfort levels in tinnitus subjects with normal and symmetric hearing thresholds are associated with a hidden injury to the cochlea that induces the development of tinnitus, especially on one side. Whether tinnitus is perceived unilaterally or bilaterally depends on the status of the auditory system, which may be reflected in the sound level tolerance and loudness discomfort levels.