Interaural Differences of Distortion Product Otoacoustic Emission Amplitudes in Patients with Unilateral Tinnitus

Objective. We aimed to determine whether abnormalities in outer hair cell (OHC) function were related to tinnitus through interaural comparison of distortion product otoacoustic emissions (DPOAEs). Study Design. Cross-sectional study. Setting. Tertiary care university teaching hospital. Participants. Twenty-seven patients with unilateral tinnitus and pure-tone average of both ears <= 25 dB hearing loss (HL) at 500, 1000, 2000, and 4000 Hz were included. Subjects and Methods. Pure-tone thresholds observed at 500 to 16,000 Hz and DPOAE amplitudes at f2 frequencies of 1001 to 6348 Hz were compared between the tinnitus ears and nontinnitus ears in patients with unilateral tinnitus. Results. The pure-tone averages (13 +/- 6 dB HL) in the nontinnitus ears were similar to those (15 +/- 6 dB HL) in the tinnitus ears. There were no differences in pure-tone averages at all frequencies tested. While the DPOAE amplitudes measured at f2 frequencies of 1001 to 3174 Hz in tinnitus ears were not different from those in the nontinnitus ears, the tinnitus ears showed significantly reduced DPOAE amplitudes when compared with the nontinnitus ears at frequencies of 4004 to 6348 Hz. Conclusion. OHC dysfunction was correlated with tinnitus at high frequencies, and DPOAE amplitudes can provide additional information about cochlear dysfunction, which is complementary to pure-tone audiometry.