Distortion products in normal hearing patients with tinnitus

Otoacoustic emissions are the result of cochlear active non-linear micromechanical mechanisms which probably originate within the OHC. OAE findings in patients with tinnitus are not univoque and there is no clear correlation between OAE modifications and tinnitus. We investigated distortion products in 20 normal hearing patients with tinnitus; all patients were selected with restrictive criteria (audiogram within 20 dB for all the frequencies, ABR and other tests normal, no history of ototoxic, nootropic drug intake, normal psychological evaluation, etc.). 12 patients out of 20 (60%) showed DP alterations. This finding is interpreted as an abnormality or a dysregulation of the efferent system (olivo-cochlear pathways) or of the other structures of the control loop which could modify outer hair cell activity in an otherwise normal cochlea with the development of tinnitus.