In two studies of patients with diabetes who did not have
neurologic symptoms, nerve conduction velocity was increased either by an improvement in
glucose control or by the administration of the
aldose reductase inhibitor
sorbinil. In a 1981 study by Graf et al,
glycemic control and motor and sensory nerve conduction velocities were evaluated in 18 patients with non-
insulin-dependent diabetes before and after one, three, six, and 12 months of
antihyperglycemic therapy. There was an improvement in motor nerve conduction velocity (median motor, p less than 0.01; peroneal motor, p less than 0.05; and tibial motor, p less than 0.05), which was associated with the improvement in fasting plasma
glucose levels after three months for some motor nerves (median motor: r = -0.62, p less than 0.01; peroneal motor: r = -0.50, p less than 0.05). A direct linear relationship between the change in fasting
glucose and
glycosylated hemoglobin levels and the change in median motor nerve conduction velocity after 12 months of
antihyperglycemic therapy was also found. Thus, there was a tendency for those patients who had the greatest improvement in
glycemic control to have the greatest improvement in motor nerve conduction velocity. The findings in the first study are consistent with the hypothesis that
hyperglycemia contributes to slowed nerve conduction velocity. In a 1983 randomized, double-blind, crossover study by Judzewitsch et al, motor and sensory nerve conduction velocities were evaluated in 39 patients with
insulin-dependent or non-
insulin-dependent diabetes in whom
glycemic control was stable. During nine weeks of treatment with 250 mg per day of
sorbinil, nerve conduction velocity was faster in the three tested nerves when compared with the velocities during the placebo period (peroneal motor nerve conduction velocity: +0.70 +/- 0.24 m per second, mean +/- SEM, p less than 0.008; median motor nerve conduction velocity: +0.66 +/- 0.27 m per second, p less than 0.005; median sensory nerve conduction velocity: +1.16 +/- 0.50 m per second, p less than 0.035). Although the effect of an improvement in
glycemic control and administration of
sorbinil in increasing nerve conduction velocity in two groups of neurologically asymptomatic patients with diabetes was small, the findings are consistent with the hypothesis that
polyol pathway activity contributes to slowed large-fiber nerve conduction velocity in these patients.