Objective: The aim of this study was to evaluate the cochlear micromechanics and central auditory function in patients with type I diabetes mellitus and to identify the site of possible dysfunction.
Methods: Cochlear activity was evaluated by recording distortion product otoacoustic emissions (DPOAEs). DPOAEs were performed using an ILO 92 Otodynamics Analyser. Functional changes in the retrocochlear auditory pathway were evaluated by auditory brainstem responses (ABRs). DPOAEs and ABRs were measured in 42 normally hearing patients with type 1 diabetes mellitus aged 21 to 42 years, and 33 age- and sex-matched nondiabetic control subjects.
Results: Both of the groups (diabetic and control) had normal and undifferentiated results in tonal and impedance audiometry. ABR peripheral transmission time (wave I) and central transmission time (interpeak latencies I-V) were significantly delayed in the diabetic compared with normal subjects, and the mean amplitudes of various DPOAEs were significantly reduced in the diabetic patients compared with the control subjects.
Conclusions: Combined use of different procedures for monitoring central and peripheral portions of the auditory pathway in diabetic patients showed alterations in cochlear micromechanics and the retrocochlear auditory pathway. Hearing impairment in diabetic patients is usually mild and subclinical, and can be detected early by accurate and objective audiometric methods.