Cystic Fibrosis Related Diabetes: A Distinct Form of Diabetes
Cystic fibrosis-related diabetes (CFRD) is a form of diabetes that is distinct from type 1 or type 2 diabetes and is common in people with cystic fibrosis (CF), an inherited disorder of the secretory glands which affects the cells that produce mucus, sweat and digestive juices.
In the past, the expected life span for a person with CF was very limited due to serious lung complications caused by the chronic disease. However, with better treatment of respiratory and other infections commonly found with the condition, individuals with CF are now living longer: the life expectancy of patients with CF has increased from less than one year in the 1950s to more than 40 years in 2013. And thus, CFRD is becoming a more common disease complication, occurring in approximately 20 percent of adolescents and 40 to 50 percent of adults with CF.
How does Cystic Fibrosis cause CFRD?
In addition to lung problems, the thick, sticky mucus produced in people with CF causes scarring and damage to the pancreas. This damage prevents the pancreas from producing enough of the hormone insulin. This is a condition known as insulin deficiency, a feature of type 1 diabetes in which antibodies attack the insulin-producing cells of the pancreas. In addition, individuals with CFRD may not respond appropriately to the insulin they make. This is known as being insulin resistant and is a feature of type 2 diabetes. Symptoms of CFRD vary from person to person. Initially, some people may not experience any symptoms until the disease worsens. Others will experience symptoms common with other forms of diabetes, such as increased thirst and urination along with unexplained weight loss.
Are the diabetes complications of CFRD different from those of typical types of diabetes?
The short answer is yes…and no! Research suggests that there might be a stronger link between fasting hyperglycemia (elevated blood sugars) and the risk of developing specific diabetes-related complications than if fasting blood sugars are normal. In a study of 37 patients with CFRD who had diabetes for more than 10 years and also had fasting hyperglycemia, 14 percent had increased urine protein (a sign of kidney damage) and 16 percent had evidence of diabetes-related eye changes (retinopathy). In another study, of 59 patients who underwent full nervous system testing, 42 percent had at least one abnormality. Gastrointestinal symptoms were found in about half of subjects both with and without fasting hyperglycemia. These symptoms were more common with longer diabetes duration or worse blood sugar control, suggesting that diabetes may aggravate the gastrointestinal abnormalities that typically underlie cystic fibrosis.
But the prevalence and severity of retinopathy and diabetes kidney disease may be lower in CFRD compared with other forms of diabetes because the hyperglycemia in those with CFRD tends to be less severe. Additionally, because those with CFRD can still be producing some insulin (the loss of production typically being slow), this factor also contributes to decreased risk of some diabetes complications. Moreover, cholesterol levels typically are low in CF, hypertension occurs but usually is mild, and insulin resistance tends to be lower unless an acute illness process occurs. Therefore, some of the metabolic factors that physicians worry about in more typical diabetes cases are less likely to be present in CFRD, lowering the risk of developing what is called large vessel disease (heart attacks, stroke and poor circulation in the legs).
How is CFRD diagnosed and treated?
CFRD is diagnosed with an oral glucose tolerance test (OGTT) performed over a two-hour period following an overnight fast. This test consists of drinking a very sweet sugar mixture, with blood tests obtained at various time intervals to check the level of sugar in the blood. The less insulin produced, the higher the blood sugar. A person without diabetes will show the same level of sugar over time, because the body makes and releases into the blood the precise insulin amount needed to keep the blood sugar normal. If there is not enough insulin, the blood sugar rises. The Cystic Fibrosis Foundation (CFF) care guidelines recommend that all individuals with CF who are 10 years of age and older be tested each year using an OGTT.
The goal of treatment is to keep the blood sugar levels as close to normal level as possible. This can be achieved through a combination of medication, dietary modification to limit sugar intake and regular exercise.
The best medication used to treat cystic fibrosis-related diabetes is insulin. There are different types of insulin that may be prescribed, including longer- and shorter-lasting formulas or a combination of the two. Other diabetes medications used to treat type 2 diabetes, such as pills and injection medications, are not recommended in treating CFRD, as the main treatment goal is to replace the insulin not being produced. Making the insulin work harder, as is typically the effect of pills, is ineffective.
Researchers worldwide are making significant progress in their understanding of cystic fibrosis and how best to treat this disease, with the goal of better treatment of the underlying cause of cystic fibrosis and CFRD, rather than just the symptoms. To learn more about CF and CFRD, visit: www.cff.org.