Evaluation of outer hair cell function and medial olivocochlear efferent system in patients with type II diabetes mellitus

AIM: This study was designed to investigate the function of outer hair cells and medial olivocochlear efferents in type II diabetes mellitus (DM). MATERIALS AND METHODS: There were 50 patients with type II DM and 51 age- and sex-matched healthy controls included in the study. Both groups were compared in terms of transient evoked otoacoustic emissions (TEOAEs), distortion product otoacoustic emissions (DPOAEs), and contralateral suppression of TEOAE. RESULTS: Pure tone thresholds of the patients with type II DM were significantly higher than in the controls (P < 0.05). The TEOAE amplitudes at 1 kHz and at 1.5, 2, 3, 4, and 6 kHz signal-to-noise ratio amplitudes on DPOAE testing were significantly lower in the patients than controls (P < 0.05). There was no significant difference between the type II DM and control groups regarding contralateral suppression test results of TEOAEs. CONCLUSION: Type II DM seems to impact the auditory system at the cochlear level by affecting the functions of outer hair cells, and it results in elevation of the thresholds on audiometry and a decrease in the amplitudes of otoacoustic emissions.