Functional Correlates of Reduced Central Conduction Velocity in Diabetic Subjects

Abstract

In a previous publication, we presented evidence of slowed conduction speed in the central nervous systems of insulin-dependent diabetic subjects, manifest in a delay in the latency of the brainstem auditory-evoked response (BAER). In this article, we present the results of a multivariate study conducted on a larger sample of 50 insulin-dependent, adult diabetic subjects. The purpose of the study was to determine some of the functional correlates of the BAER delay; each patient received an assessment of the BAER, the late auditory-evoked potential (EP), the conduction velocities of the sural, median, and common peroneal nerves, and intellectual and emotional function, in addition to neurologic and audiologie examinations. A nondiabetic control group was matched with the diabetic group as to age and sex. The results indicated a delay in the latency of wave V, and in interpeak latencies I–III and I–V, of the BAER. The most reliable effect was on interpeak latency I–V; this suggested that the locus of the delay was in the central auditory projections, rather than in the acoustic nerve. In addition, BAER waves I, II, III, IV, and V were reduced in amplitude, as was the Ni component of the late auditory EP; the most reliable reduction in amplitude was in wave V. The effect was similar in magnitude for males and females, relative to their counterparts in the control group. The slowed BAER response appeared early in the disease and was not related to the duration of insulin treatment. It was correlated with a chronic loss of energy and the presence of sexual dysfunction. It was not correlated with intellectual deterioration, clinical signs of peripheral or autonomie neuropathy, recent blood sugar regulation, or current blood sugar levels. The results of this study confirm the presence of abnormalities in the central nervous systems of diabetic subjects, and suggest that the BAER technique may prove useful in detecting early signs of central diabetic neuropathy.