Contralateral suppression of otoacoustic emission in subject with tinnitus

Abstract

Objectives: The medial olivocochlear bundle effect is studied through the suppression of otoacoustic emissions and seems to be influenced by the laterality of the central nervous system, although this fact was not considered in many previous studies. Once dysfunctions of such regulating system may be involved in the generation of tinnitus, the objective of this study is to analyze this suppression in tinnitus patients and the influence of functional laterality upon this test. Methods: Forty-four patients with tinnitus and 44 without tinnitus underwent suppression of distortion product otoacoustic emissions. The suppression effect was calculated by subtracting the value of otoacoustic emissions obtained at the 1000 to 6000 Hz frequency range without contralateral noise from that obtained with contralateral noise. Only the results of the right ears were considered for analysis in each group. Afterwards, comparison between the results of right and left ears of the control group was performed to evaluate the influence of functional laterality over the suppression. Results: The results observed among subject with and without tinnitus showed an association between absence of contralateral suppression and presence of tinnitus at all frequencies studied (OR >2.1). The results obtained from the right and the left ears of subject without tinnitus showed higher right-side suppression at 1000 Hz, 2000 Hz, 3000 Hz, 4000 Hz. Conclusion: There was a clear correlation between diminished effectiveness of the medial olivocochlear bundle and the presence of tinnitus. The central nervous system laterality should be a controlled variable in the study of the functions of such pathways.