To Örebro University

Background and Aim: The medial olivocochlear (MOC) system contributes to better sound perception and distinction in noisy environments by causing an inhibitory effect on the cochlear hair cell system. The aim of this study is to search for possible involvement of olivocochlear dysfunction in the generation of tinnitus. The function of the MOC system was evaluated by contralateral suppression (CS) of the TEOAEs and DPOAEs.

Material and Methods: Seventeen patients with bilateral tinnitus (6 men, 11 women; mean age, 46.8 years), 16 patients with left unilateral tinnitus (7 men, 9 women; mean age, 51.1 years), and a control group (CG) of 15 people (7 men, 8 women; mean age, 40.5 years) without tinnitus were included in this study. All the subjects were right-handed with normal pure tone audiogram and without any other underlying pathology. The subjects were evaluated with TEOAEs and DPOAEs without and with the presence of contralateral white noise of 50 dB. The frequencies measured were 1–4 kHz for the TEOAEs and 1–6 kHz for the DPOAEs.

Results: Bilateral tinnitus individuals tended to present less suppression than the CG subjects (presence of suppression 32.3–60%, depending on the frequency, for the tinnitus group vs. 66.6–90% for the CG), and lower volume of suppression than the CG subjects (1.3–2.22 dB vs. 2.47–4.66 dB, depending on the frequency). Similar results were observed in patients with left unilateral tinnitus—presence of suppression in their left ears from 31.2–75% and mean value of suppression 0.62–3.38 dB, whereas 73.3–100% of the left ears of the CG presented suppression with mean value of 2.85–5.38 dB. The differences regarding the right ear were less marked.

Conclusions: Contralateral suppression is lower and less frequent in ears with tinnitus compared with normal ears. This may reflect a disfunction of MOC in patients with tinnitus. Both TEOAEs and DPOAEs seem to be sensitive methods to confirm this relation.