Cochlear dysfunction and diabetic microangiopathy

The aim of this study was to evaluate the cochlear micromechanics in type 1 diabetic patients and to compare these findings with diabetic microvascular complications (retinopathy and nephropathy). Cochlear activity was evaluated by recording 2f1-f2 DPOAE. DPOAEs were performed using an ILO92 Otodynamics Ltd Analyser. DPOAEs were measured in 42 normally hearing IDDM patients aged between 21 and 42 years, and 33 age-and sex-matched non-diabetic control subjects. IDDM patients were divided into two groups: 17 patients without microangiopathy and 25 with microangiopathy. Microangiopathy was evaluated with ophthalmoscopy and 24-hour albumin excretion rate into urine. Both groups (diabetic and control) had normal and undifferentiated results in tonal and impedance audiometry. The mean amplitudes of various DPOAEs were significantly reduced in the diabetic groups (with and without microangiopathy) compared with control subjects. No correlation was found between diabetic microvascular complications and DPOAE amplitudes reduction. Our results indicate the existence of an alteration in cochlear micromechanics in diabetic patients with microangiopathy as well as in patients without microangiopathy. The lack of significant correlation between the degree of microvascular complications in the retina or kidneys and DPOAEs amplitude reduction suggest that the impaired functional properties of the outer hair cells are probably caused by early metabolic complications in diabetes (among other things non-enzymatic glycation related to hyperactivity of free oxygen radicals) and not directly by diabetic microangiopathy.