Insulin therapy in patients with cystic fibrosis related diabetes mellitus: benefit, timing of initiation and hypoglycaemia

Pancreatic endocrine dysfunction in patients with cystic fibrosis heralds declining pulmonary function and a six-fold rise in mortality. Insulin therapy increases weight and reduces decline in lung function. Optimal timing of initiation remains contentious but early intervention may maximise benefit. We explored the optimal timing of initiation of therapy and characterised the frequency and usual symptoms of hypoglycaemia. Fifty-four patients with cystic fibrosis treated with insulin were compared up to five years pre and post insulin initiation with respect to weight gain and lung function. Frequency and usual symptoms of hypoglycaemia were assessed using the Hypoglycemia Symptoms Awareness Questionnaire. Mean age was 27.6(16–52) years. In the five years preceding insulin therapy, FEV1 declined from 2.6±0.14L to 1.78±0.12L (p<0.001). In the group as a whole, rate of decline was arrested with insulin initiation; the mean five-year post insulin FEV1 was 1.74±0.20L (p=0.15). When stratified according to oral glucose tolerance testing at initiation the rate of decline was significant in patients with impaired glucose tolerance (p=0.02) but not normal glucose tolerance nor overt cystic fibrosis diabetes mellitus. Insulin therapy increased weight from 53.08±1.53kg to 56.22±2.08kg (p=0.05). Hypoglycaemia was common and 75% of respondents scored results indicative of hypoglycaemia unawareness. This study confirms that the favourable effect of insulin upon lung function in patients with cystic fibrosis correlates with the degree of glucose intolerance at baseline. Hypoglycaemia is an important clinical issue. Copyright © 2011 John Wiley & Sons.