Auditory brainstem-evoked responses (ABR) were recorded from the scalp of 30 normoacoustic insulin-dependent diabetic subjects, aged between 15 and 41 yr (29 ± 7 yr). Three different stimulus repetition rates (11, 37, and 87 cps) were used. The results were compared with those obtained from 20 age- and sex-matched, normoacoustic control subjects. In diabetic patients, metabolic control (mean daily plasma glucose, glycosylated hemoglobin) and the presence of retinopathy, nephropathy, and somatic neuropathy were also investigated. The latencies (ms) of ABR waves were significantly impaired in diabetic subjects as compared with normals. Peripheral transmission time (wave I) and central transmission time (waves I–V) were also significantly delayed in diabetic subjects. Moreover, by increasing stimulus repetition rates, a significant increase in waves I–V shift was observed in diabetic patients. ABR impairment was not related to glucose balance, to the duration of diabetes, or to the presence of the diabetic retinopathy, nephropathy, and somatic neuropathy.
In conclusion, diabetic neuropathy is characterized not only by somatic and autonomie nerve dysfunctions, but also by the early involvement of the central nervous system (CNS). ABR recording can represent a useful, noninvasive, simple procedure to detect both acoustic nerve and CNS damage.