Effect of Prior Intensive Insulin Treatment During the Diabetes Control and Complications Trial (DCCT) on Peripheral Neuropathy in Type 1 Diabetes During the Epidemiology of Diabetes Interventions and Complications (EDIC) Study

OBJECTIVE - To evaluate the impact of former intensive versus conventional insulin treatment on neuropathy in Diabetes Control and Complications Trial (DCCT) intensive and conventional treatment subjects with type 1 diabetes 13-14 years after DCCT closeout, during which time the two groups had achieved similar A1C levels. RESEARCH DESIGN AND METHODS - Clinical and nerve conduction studies (NCSs) performed during the DCCT were repeated during the Epidemiology of Diabetes Interventions and Complications (EDIC) study by examiners masked to treatment status on 603 former intensive and 583 former conventional treatment subjects. Clinical neuropathy was defined by symptoms, sensory signs, or reflex changes consistent with distal polyneuropathy and confirmed with NCS abnormalities involving two or more nerves among the median, peroneal, and sural nerves. RESULTS - The prevalence of neuropathy increased 13-14 years after DCCT closeout from 9 to 25% in former intensive and from 17 to 35% in former conventional treatment groups, but the difference between groups remained significant (P < 0.001), and the incidence of neuropathy remained lower among former intensive (22%) than former conventional (28%) treatment subjects (P = 0.0125). Analytic models of incident neuropathy that adjusted for differences in NCS results at DCCT closeout showed no significant risk reduction associated with former intensive treatment during follow-up (odds ratio 1.17 [95% CI 0.84-1.63]). However, a significant persistent treatment group effect was observed for several NCS measures. Longitudinal analyses of overall glycemic control showed a significant association between mean A1C and measures of incident and prevalent neuropathy. CONCLUSIONS - The benefits of former intensive insulin treatment persisted for 13-14 years after DCCT closeout and provide evidence of a durable effect of prior intensive treatment on neuropathy.