Study Examines Modern-Day Course of Type 1 Diabetes

The rates of serious complications among individuals with type 1 diabetes appear lower than reported historically, especially when patients are treated intensively, according to a report in the July 27 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

“The clinical course of type 1 diabetes mellitus, including its treatment, metabolic outcomes and long-term clinical complications, has changed dramatically in the past 20 years,” the authors write as background information in the article. Treatment innovations, including insulin pumps and analogues, along with the improved treatment of co-occurring illnesses such as high blood pressure and abnormal cholesterol have contributed to changes in the management of type 1 diabetes.

In addition, clinical trials such as the Diabetes Control and Complications Trial (DCCT)—a study conducted between 1983 and 1993 comparing the then-current standard of care with more intensive therapy—and its long-term observational follow-up, the Epidemiology of Diabetes Interventions and Complications (EDIC) study, have shown the benefits of more careful control of blood glucose levels.

The DCCT/EDIC Research Group analyzed the incidence of long-term complications among participants in those studies, including both patients who were originally assigned to intensive therapy and those who received standard therapy until the DCCT clinical trial ended in 1993 and all patients were offered intensive therapy. In addition, they assessed complication rates among participants in the Pittsburgh Epidemiology of Diabetes Complications study, an observational study in which researchers have collected data on patients who were diagnosed with type 1 diabetes between 1950 and 1980.

“After 30 years of diabetes, the cumulative incidences of proliferative retinopathy [an eye disease associated with diabetes], nephropathy [kidney disease] and cardiovascular disease were 50 percent, 25 percent and 14 percent, respectively, in the DCCT conventional treatment group, and 47 percent, 17 percent and 14 percent, respectively, in the Pittsburgh Epidemiology of Diabetes Complications cohort,” the authors write. “The DCCT intensive therapy group had substantially lower cumulative incidences (21 percent, 9 percent and 9 percent) and fewer than 1 percent became blind, required kidney replacement or had an amputation because of diabetes during that time.”

Differing methods of ascertaining and defining complications make exact historical comparisons difficult. However, the rates of retinopathy (30 percent) and nephropathy (12 percent) in DCCT/EDIC participants after 25 years compare favorably to rates in studies of individuals who developed diabetes 10 to 20 years prior (40 percent to 53 percent for retinopathy and approximately 35 percent for nephropathy). Rates of functional impairment, such as vision loss and the need for kidney transplant, are also difficult to compare but were low in the overall DCCT/EDIC cohort, with only three of 1,441 patients becoming legally blind and 18 requiring kidney replacement therapy after an average of 25 years.

“While the results of the DCCT/EDIC conventional therapy and of the Pittsburgh Epidemiology of Diabetes Complications study supply clinicians with a realistic description of clinical outcomes that they can discuss with their patients who have had their type 1 diabetes mellitus in the past 25 years, the intensive treatment group results provide a view of what patients with type 1 diabetes mellitus can expect in the future. Intensive therapy, now the standard of care, should result in more than 50 percent reduction in the rates of complications over time, with implementation early in the course of diabetes providing the most powerful salutary effect.”

Arch Intern Med. 2009;169[14]:1307-1316.