[Effect of diabetic control on the progression of neuropathy]

We investigated the relationship between blood levels of HbA1, an indicator of diabetic control, and the polyneuropathy index (PNI), an indicator of diabetic polyneuropathy. A total of 175 patients with non-insulin-dependent diabetes mellitus were followed for more than 3 years and were subjected to a series of motor conduction studies every 1 to 3 years. The PNI was calculated as a mean percentage of normal values for 12 indices derived from the conduction velocity and long-distance latency in motor conduction studies of 4 nerves. The mean follow-up period was 5.0 years, and during that time the mean decrease in the PNI was 2.7%. There was a significant negative correlation between mean HbA1 levels (X) and the percent changes in PNI per year (Y), and the equation for the regression line was Y = -0.102X + 0.37 (r = 0.283, p < 0.001). The higher the HbA1 level during this period, the larger the decline in PNI was. In patients with low initial PNI levels the change in PNI tended to be small in spite of high HbA1 levels. Likewise, in patients with high initial PNI levels the decrease in PNI tended to be large despite relatively good control of their HbA1 levels. However, since there were many patients whose HbA1 levels were not correlated with the reduction in PNI, there may be some unknown factors, possibly genetic, that play a role in the progression of polyneuropathy in diabetic patients.