Effects of one year of near-normoglycemia on peripheral nerve function in type 1 (insulin-dependent) diabetic patients

Summary Ninety poorly controlled C-peptide negative type 1 (insulin-dependent) diabetic patients with chronic complications were allocated to intensified insulin treatment with either continuous subcutaneous insulin infusion or multiple insulin injections; 83 were studied over 1 year (seven patients dropped out of the study). Peripheral nerve function was assessed by clinical examination, malleolar vibration perception threshold, and motor and sensory nerve conduction velocities (MNCV; SNCV) in the median, ulnar, peroneal, and sural nerves. In order to assess the effect of metabolic control on peripheral nerve function, the results in patients with normal mean HbA₁ levels during months 3–12 of the study <8.6% (tight control (tc);n=50) were compared with those with abnormal mean HbA₁ 8.6% (poor control (pc);n=33). Mean blood glucose was significantly higher in pc than in tc at months 2–9 and 11 (P<0.05). In pc median and ulnar SNCV were significantly lower at 6 and 12 months, and ulnar and peroneal MNCV at 12 months than in tc (P<0.05). No significant differences between the groups were observed for median MNCV, sural SNCV, and vibration sensation. Further analysis revealed that in well-controlled patients who showed abnormal peripheral nerve tests at baseline, median, and ulnar MNCV and SNCV but not peroneal MNCV, sura SNCV, and vibration sensation were significantly improved after 12 months as compared with poorly controlled patients with initially abnormal tests (P<0.05). There were no differences in nerve function between well- and poorly-controlled patients who had normal nerve tests at baseline. These results provide evidence that near-normoglycemia over 1 year does not have uniform effects on peripheral nerve function in type 1 diabetic patients. Impaired motor and sensory nerve conduction seems to be more susceptible to improvement under strict glycemic control in the upper than in the lower extremities.Abbreviations at Abnormal tests - CSII Continuous subcutaneous insulin infusion - GM Geometrical mean - ICT Intensified conventional therapy - MNCV Motor nerve conduction velocity - pc Poor control - SEF Standard error factor - SNCV Sensory nerve conduction velocity - tc Tight control - VPT Vibration perception threshold Members of the Study Group: H. Berger, I. Cicmir, K. Dannehl, K. Dopstadt, F.A. Gries (coordinator), A. Hübinger, Th. Koschinsky, P. Mayer, W. Schäfer, B. Schleppinghoff, M. Toeller, D. Tschöpe, K. Wiefels, and D. Ziegler