Diabetes mellitus is an increasingly recognized problem as survival in patients with cystic fibrosis improves. Up to 15% of children and adults attending cystic fibrosis clinics are found to have diabetes.
The main cause of CF related diabetes is destruction of the pancreas due to fibrosis. Islet cells which produce insulin are therefore depleted. In addition recurrent infection causes physical stress and insulin resistance. This is often variable and it is not uncommon to have higher blood sugar levels during times of physical stress.
CFRD has characteristics of both type 1 and type 2 diabetes. Lack of insulin is the primary problem and people are usually slender rather than obese. However is recognised to be a distinct form of diabetes that requires a special management approach.
The average age of onset of CFRD is 18-21 years. Onset is often insidious and one may have diabetes for several years without knowing. In one series almost 30% of patients with CFRD did not have symptoms of hyperglycaemia or unexplained weight loss presentation.
The criteria used to diagnose CFRD are the same as those used for diabetes mellitus. Presentation with ketoacidosis is rare.
The management of CFRD is complex and best undertaken by a diabetes team comprising of a diabetes specialist Physician or Paediatrician, Diabetes Nurse, Dietician with close support from family. This team should have close links with the Chest team. Most patients with high blood sugars will require insulin therapy.
Treatment with insulin usually leads to weight gain and improvement in general well being and energy levels.
Dietary recommendations in CFRD is different from type 1 and type 2 diabetes. Conventional 'diabetic diets' which are used in some non-CF diabetes would be entirely inappropriate in CFRD.
It is important to eat enough calories to achieve normal weight and growth. It is not unusual to advise a high energy intake with increased carbohydrates aiming for 120 –150% of recommended energy intake for age and sex. A diet high in fat may also be advised (40% of energy intake).
It is impossible to provide universal dietary recommendations and the input of an experienced dietician is essential.
Blood sugars can rise significantly during acute illness and require close monitoring and adjustment of insulin doses.
Regular snacks may be required to prevent hypoglycaemia.
Microvascular complications of diabetes are now being recognised due to people with CF having a longer life expectancy.
Cystic Fibrosis Trust - www.cftrust.org.uk
Dr Nishan Wijenaike
West Suffolk Diabetes Service