No correlation between impairment of cerebrovascular reserve capacity and electrophysiologically assessed severity of neuropathy in noninsulin-dependent diabetes mellitus

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Introduction: Microvascular abnormalities have an important role in the most frequent neurological complications of diabetes mellitus: neuropathy and cerebrovascular disorders. Severity of neuropathy as well as of cerebral microvascular damage can be quantitatively evaluated by instrumental methods like nerve conduction studies and transcranial Doppler. In the present study, we investigated whether a correlation exists between the severity of peripheral neuropathy and the impairment of cerebrovascular reserve capacity (CRC) in 20 patients with Type 2 diabetes mellitus. Methods: CRC was measured by transcranial Doppler and defined as the maximal percentage increase in blood flow velocity in the middle cerebral artery within 20 min after an intravenous dose of 1000 mg of acetazolamide. Nerve conduction studies of the median, ulnar, peroneal, and sural nerves were performed. Severity of neuropathy was scored based on conduction velocities, amplitudes, and distal latencies. Results: There was no correlation between the neuropathic score and CRC ( R=.003, P=.99). Neither CRC nor the neuropathic score correlated significantly with age, duration of diabetes, and serum values of HbA 1c, glucose, insulin, von Willebrand factor, and α 2-macroglobulin. Severity of neuropathy but not CRC correlated with microalbuminuria ( R=.47, P=.038 and R=.14, P=.54). Improper treatment reflected by HbA 1c>10% was associated with significantly more severe albuminuria, higher actual blood glucose level, higher von Willebrand factor activity, and marginally higher neuropathic score (21 vs. 13, P=.096), but was not associated with CRC (44% vs. 42%, P=.81). When duration of diabetes was dichotomized to 15 years and less or over 15 years, CRC was significantly smaller (35% vs. 50%, P=.036) and neuropathy was more severe in the subgroup with longer diabetes duration (19 vs. 11.5 points, P=.07). Conclusions: Although both CRC and peripheral nerve function are affected more severely in patients with long-lasting Type 2 diabetes mellitus, damage in the cerebrovascular system and in the long peripheral nerves occur independently. As in diabetes mellitus pathological changes in autonomic and large peripheral nerves develop simultaneously, decreased CRC in diabetic patients might be predominantly due to structural changes of resistance arteries or to metabolic than to neurogenic factors.