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Abstract and Introduction
Abstract
Objective To describe the development and progression of neuropathy and related findings among patients with type 1 diabetes who participated in the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) study.
Research Design and Methods The main diabetic peripheral neuropathy (DPN) outcome was assessed using clinical symptoms, signs, and nerve conduction study results during DCCT and repeated in EDIC year 13/14. Cardiovascular autonomic neuropathy (CAN) was assessed by R-R response to paced breathing, Valsalva ratio, and blood pressure response to standing during DCCT and in EDIC years 13/14 and 16/17. Additionally, symptoms reflecting neuropathic pain and autonomic function (including hypoglycemia awareness) were collected yearly in EDIC using standardized questionnaires; peripheral neuropathy was also assessed annually using the Michigan Neuropathy Screening Instrument. Assessments of genitourinary function were collected at EDIC year 10.
Results Intensive therapy during the DCCT significantly reduced the risk of DPN and CAN at DCCT closeout (64% and 45%, respectively, P < 0.01). The prevalence and incidence of DPN and CAN remained significantly lower in the DCCT intensive therapy group compared with the DCCT conventional therapy group through EDIC year 13/14.
Conclusions The persistent effects of prior intensive therapy on neuropathy measures through 14 years of EDIC largely mirror those observed for other diabetes complications. DCCT/EDIC provides important information on the influence of glycemic control, and the clinical course of diabetic neuropathy, and, most important, on how to prevent neuropathy in type 1 diabetes.
Introduction
The Diabetes Control and Complications Trial (DCCT) enrolled 1,441 patients with type 1 diabetes between 1983 and 1989. At study entry, participants were randomly assigned to intensive insulin therapy (INT), targeting near-normal glycemia, or conventional insulin therapy (CON) according to the standard of care at that time. Microvascular diabetes complications were assessed during the DCCT, including the development and progression of the peripheral and cardiovascular autonomic manifestations of diabetic neuropathy. In 1993, after an average of 6.5 years of follow-up, the DCCT investigators reported that INT significantly reduced the incidence of diabetic neuropathy, similar to findings for diabetic retinopathy and nephropathy. INT was subsequently widely accepted as the standard of care for type 1 diabetes. At DCCT end, DCCT CON participants were taught INT, and all participants were encouraged to adhere as closely as possible to an intensive diabetes treatment regimen and were returned to their prior health care providers for ongoing care. The observational Epidemiology of Diabetes Interventions and Complications (EDIC) follow-up was established to monitor the long-term effects of prior INT compared with prior CON treatment on the development and progression of more advanced microvascular complications and cardiovascular disease in the DCCT cohort.
Diabetic neuropathy represents a clinically diverse group of disorders having differing anatomic distribution, clinical course, and underlying pathophysiology, but ultimately thought to reflect metabolic and microvascular factors that result in axonal degeneration of large- and small-nerve fibers. The specific presentation of diabetic neuropathy reflects the distribution and size of nerve fibers involved, most commonly presenting as a distal symmetric sensory or sensorimotor neuropathy (diabetic peripheral neuropathy [DPN]). Manifestations of autonomic neuropathies, including cardiovascular autonomic neuropathy (CAN), may also develop. Although the specific clinical manifestations are heterogeneous, diabetic neuropathy is a major cause of disability, associated with reduced quality of life and high mortality. In this article, we detail and discuss the diabetic neuropathy outcomes, including DPN and CAN, during DCCT/EDIC.
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