Critical clinical changes of pulmonary function and weight occur in patients with cystic fibrosis (CF) antecedent to the development of frank Diabetes Mellitus (DM). Impaired glucose tolerance (IGT) signifies diminished Insulin secretion and increased peripheral insulin resistance, correlating with worse clinical status, under nutrition and impaired pulmonary function. Insulin therapy has been associated with improvement in anthropometric data and an arrest in decline in forced expiratory volume in 1 second (FEV1). Timing of initiation remains contentious and it has been postulated that early intervention may maximise benefit.
We preformed a retrospective analysis of clinical outcome correlating baseline 75 g OGTT with weight and pulmonary function up to 5 years before and after Insulin initiation in 54 Insulin treated patients with CF. The mean age of the patients was 27.64 years, range 1652, and HbA1c 6.56%. Mean duration on Insulin was 5.78 years (4 months to 29 years). 37% were on prandial Insulin, 37% on a twice daily prefixed mixture, 20% on a basal bolus regimen and 6% on once daily basal Insulin.
When grouped together during the 5 years proceeding Insulin initiation FEV1 declined from 2.6±0.14 L to 1.78±0.12 L (P<0.001), a trend arrested by Insulin treatment (mean 5 year post Insulin FEV1 1.74±0.20 L (P=ns)). When stratified to baseline OGTT the effect on rate of decline in FEV1 was significant in patients with IGT (pre Insulin change in FEV1 0.51±0.31 L vs post Insulin FEV1 0.04±0.12 L, P=0.02) but not normal glucose tolerance (P=0.86) nor overt CFDM (P=0.70). Insulin therapy significantly increased weight from 53.08±1.53 Kg to 56.22±2.08 Kg (P=0.05).
These data confirm that the beneficial effect of Insulin within this patient group is most prominent early, within patients with IGTT.