The Effect of Tinnitus and Presbycusis on Contralateral Suppression of Otoacoustic Emissions

Background The medial olivocochlear system (MOCS), part of the efferent auditory pathway, causes an inhibitory effect on the outer hair cells, thus protecting them against extreme noise exposure and improving speech discrimination in noisy environments. This study aims to assess the MOCS function and aging in tinnitus patients with the use of contralateral suppression (CS) of otoacoustic emissions (OAEs). Material and Methods 136 subjects took part in this study, divided in 6 groups (control group, right-side tinnitus, left-side tinnitus, bilateral tinnitus, presbycusis without tinnitus and presbycusis with tinnitus). CS of transiently- evoked (TEOAEs) and distortion products OAEs (DPOAEs) was measured for each group and pair- wise comparisons between the groups were performed. Results CS was less frequent and the mean values of CS were significantly lower in the tinnitus ears than normal ones. The mean values of CS of ears with presbycusis were in some cases higher than ears with presbycusis and tinnitus and also than ears with tinnitus and normal hearing. Not particular statistical differences were found between the method used (TEOAEs or DPOAEs) and the comparisons between the groups. Conclusions The absence and lower values of CS in tinnitus ears imply a MOCS dysfunction as a main factor of tinnitus generation. Tinnitus seems to have a more detrimental effect to the MOCS function than presbycusis. CS of TEOAEs and DPOAEs are equally sensitive methods in detecting MOCS dysfunction in patients with tinnitus.