Involvement of central nervous system in patients with diabetes mellitus detected by evoked potentials

Somatosensory (SSEPs) and brainstem auditory evoked potentials (BAEPs) were recorded for 44 patients with diabetes mellitus (age, 63.0 +/- 9.3 years, mean +/- SD) and 20 age-matched healthy controls (age, 67.3 +/- 9.1 years) to elucidate the involvement of the central nervous system (CNS) in diabetes mellitus. Furthermore, relationships between SSEP or BAEP and clinical variables such as autonomic nervous function, peripheral nerve conduction velocity, duration of diabetes, metabolic control (fasting blood sugar level, HbA1 and HbA1c levels) and therapeutic method, were studied. The central conduction time (CCT), which represents the peak latency between N13 and N20, in patients with diabetes mellitus was significantly longer than that of the healthy controls (p less than 0.005). Likewise, diabetic patients showed significant prolongation of interpeak latency between waves I and V (I-V IPL) compared to the healthy controls (p less than 0.005). Significant correlations between CCT and motor conduction velocity of median nerve (p less than 0.05) were observed although the correlation between CCT and sensory nerve conduction velocity was not found to be significant (p less than 0.1). Furthermore, I-V IPL was significantly correlated with the duration of illness (p less than 0.05). There were no significant correlations between CCT or I-V IPL and autonomic nervous dysfunction as determined by orthostatic hypotension and the coefficient variation of the R-R interval or metabolic control or therapeutic method. From the present results, it would appear that there is CNS involvement even in diabetic patients not manifesting overt CNS signs and symptoms and that it is correlated somewhat with impairment of the peripheral nervous system and duration of illness.