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

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

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.

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.

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.