Cystic fibrosis-related diabetes mellitus: clinical impact of prediabetes and effects of insulin therapy

In patients with cystic fibrosis (CF), glucose intolerance preceding diabetes (prediabetes) may have adverse effects on nutritional status and respiratory function, which are reversible after the start of insulin therapy. Respiratory function (forced vital capacity and forced expiratory volume in one second) and body mass index (BMI) were compared retrospectively in a French cohort of 14 patients during the 5 y preceding insulin therapy for diabetes and in 14 age- and sex-matched controls with normal oral glucose tolerance tests. In the diabetic group, all three parameters deviated increasingly from the values in the controls, the differences became statistically different during the 6 mo before insulin therapy. The effect was more important in patients for whom diabetes mellitus was diagnosed on the basis of symptoms or hyperglycaemia than in patients for whom it was diagnosed by systematic screening, but still present in the latter. After insulin was started, respiratory function improved and the BMI returned to normal within 1 y. The annual insulin requirement increased from 0.62 during the first year to 1.25 during the fifth year. Glycosylated haemoglobin (HbA(1c)) values ranged from 6.6 to 7.8%. Only 2 episodes of severe hypoglycaemia were recorded over 42 patient-years or follow-up. The insulin regimen most often used was two daily injections of a mixture of short- and intermediate-acting insulin (n = 10) given with an insulin pen. Conclusion: The clinical status of CF patients who will need insulin therapy deteriorates before the start of insulin. In patients with CF-related diabetes, with or without fasting hyperglycaemia, insulin therapy improves anabolism and provides good glycaemic control with few severe hypoglycaemic episodes.