Evaluation of cochlear function in patients with normal hearing and tinnitus: a distortion product otoacoustic emission study.

Objectives: We investigated cochlear function in normal-hearing patients with tinnitus using distortion product otoacoustic emissions (DPOAE).

Patients And Methods: The study included 20 normal-hearing patients with tinnitus (13 males, 7 females; mean age 25 years; range 17 to 52 years) and 15 controls (10 males, 5 females; mean age 23 years; range 18 to 27 years) with normal hearing. Both groups underwent routine audiological tests including audiometry and tympanometry. Cubic DPOAEs were recorded from both groups. Signal-to-noise ratios (SNRs) lower than the 10th percentile of the control values were regarded as abnormal or undetectable.

Results: Tinnitus was bilateral in seven patients and unilateral in 13 patients. Seven patients with unilateral tinnitus and all patients with bilateral tinnitus had a history of exposure to noise. The mean perceived frequencies for tinnitus were 6.3 kHz and 6.2 kHz in the left and right ears, respectively. Loudness was measured as 8 dB SL in the left ears, and 7 dB SL in the right ears. Compared to unilateral cases, patients with bilateral tinnitus exhibited a higher percentage of abnormal SNRs at most frequencies. Some asymptomatic ears in the patient group had abnormal results.

Conclusion: These findings show that tinnitus in normal-hearing patients is often associated with varying degrees of cochlear dysfunction. The results also suggest that tinnitus may be regarded as an early manifestation of noise-induced hearing loss in patients with a history of exposure to noise.