Evaluation of hearing system by contralateral suppression test and evoked otoacustic emissions in Type II diabetes mellitus

This study was designed to investigate the auditory system functions of the olivocochlear efferents in the Type II DM. 50 patients who had type II DM, normal otoscopic findings and a PTA better than 30 dB on audiometry, and 51 age and sex matched healthy controls were included in the study. Both groups were compared in terms of TUOAE, DPOAE and TUOAE with contralateral suppression, using ILO292 version 6 model device. Audiogram thresholds of the Type II DM patients were found statistically significantly high according to the control (p<0.05). 1000 Hz amplitudes of the TUOAE test , 1500, 2000, 3000, 4000, 6000 Hz SGO amplitudes of the DPOAE test were found statistically significantly low according to the control cases (p<0.05). TUOAE, DPOAE tests are affected from age and gender. Audiometry, TUOAE and DPOAE results of the female diabetics were better than male diabetics.There was no statistically significant difference between Type II DM and control group regarding contralateral suppression test results. Type II DM seems to impact on the auditory system at the cochlear level by affecting the functions of OHCs, and results in elevation of the thresholds on audiometry and loss of the emissions. DPOAE testing is more sensitive to the cochlear damage than TUOAE testing as the DPOAEs are affected early in the course of Type II DM. No data was found to present that medial olivocochlear system is affected in Type II DM.KEY WORDS: Diabetes mellitus, medial olivocochlear system, contralateral suppression, hearing, otoacoustic emissions