Distortion-Product Otoacoustic Emissions and Selective Sensorineural Loss in IDDM

OBJECTIVE To provide information about possible subclinical damage of the cochlear outer hair cells (OHCs) by means of transiently evoked otoacoustic emissions (TEOAEs) and distortion-product otoacoustic emissions (DPOAEs) in subjects with IDDM. RESEARCH DESIGN AND METHODS TEOAEs and DPOAEs were recorded in 47 IDDM patients with normal hearing and in age- and sex-matched nondiabetic subjects. Peripheral neuropathy was diagnosed by nerve conduction velocity (NCV) at the peroneal and surral nerves. RESULTS A subclinical peripheral neuropathy was found in 15 diabetic patients. Mean TEOAE amplitude was found to be significantly reduced in diabetic patients with a reduced NCV (7.6 ± 3.2 dB; Scheffé's test: P = 0.03), but not in those without neuropathy (9.5 ± 4.3 dB), with respect to control subjects (11 ± 3.1 dB). Neuropathic patients also showed mean reduced DPOAE amplitude values in the region of middle and high frequencies from 1,306 to 5,200 Hz (P < 0.05), whereas no difference was found at the lowest-frequency amplitudes. A frequency-selective reduction of DPOAEs was also found in non-neuropathic patients (P < 0.05) in the region of higher frequencies at 3,284, 4,126, and 5,200 Hz compared with control subjects. No correlations were found among duration of diabetes, HbA1c values, TEOAEs and DPOAEs. CONCLUSIONS Our results suggest that IDDM patients show an early abnormality of the micromechanical properties of the OHCs. In IDDM patients without a subclinical peripheral neuropathy, damage is limited to the higher frequencies and can be detected only by DPOAEs, whereas in IDDM patients with neuropathy, damage also involves the middle range of frequencies and can be detected by TEOAEs and DPOAEs. Therefore, DPOAEs seem to be able to detect the earliest cochlear selective-frequency dysfunction in IDDM patients without peripheral neuropathy. DPOAEs appear to be of greater clinical interest than TEOAEs; the former seem to be frequency specific and can be recorded at any chosen frequency, including high frequencies.