Lung Transplantation and the Development of Diabetes Mellitus in Adult Patients With Cystic Fibrosis

Cystic fibrosis related diabetes (CFRD)--the end stage of progressive insulin deficiency

In cystic fibrosis, gradual pancreatic destruction causes progressive insulin deficiency, culminating in cystic fibrosis related diabetes (CFRD). As a consequence of insulin deficiency, elevated glucose levels can be detected (well before the diagnosis of CFRD), by continuous ambulatory subcutaneous interstitial fluid glucose monitoring or 30-min sampled oral glucose tolerance test (OGTT). Current diagnostic criteria for CFRD (based on 0 and 120-min OGTT blood glucose levels) were originally designed to forecast microvascular disease in type 2 diabetes, rather than CF-specific outcomes such as declining weight or lung function. In CF, decline in either weight or lung function predicts early mortality. Both may precede the diagnosis of CFRD by several years. Insulin, a potent anabolic hormone, is recommended treatment for CFRD, but use in earlier stages of insulin deficiency is not established. Conventional dosing (with four or more insulin injections per day) is burdensome and carries substantial risk of hypoglycemia. However, recent uncontrolled trials suggest that once-daily injection of intermediate or long-acting insulin improves weight and lung function, with minimal hypoglycemia risk, in CFRD and also in early insulin deficiency. It is plausible that insulin may be of greater benefit to respiratory function when given prior to the diagnosis of CFRD, after which structural lung disease may be irreversible. It is also plausible that early insulin treatment may prolong the lifespan of the remaining insulin-secreting β-cells. Randomized controlled trials are now needed to determine whether or not current clinical practice should be altered toward the earlier commencement of insulin in CF.

Symposium 6: Young people, artificial nutrition and transitional care The nutritional challenges of the young adult with cystic fibrosis: transition

Cystic fibrosis (CF) is a complex multisystem disorder affecting mainly the gastrointestinal tract and respiratory system. Intestinal malabsorption occurs in approximately 90% of patients. In the past, malnutrition was an inevitable consequence of disease progression, leading to poor growth, impaired respiratory muscle function, decreased exercise tolerance and immunological impairment. A positive association between body weight and height and survival has been widely reported. The energy requirements of patients with CF vary widely and generally increase with age and disease severity. For many young adults requirements will be 120–150% of the age-related estimated average requirement. To meet these energy needs patients are encouraged to eat a high-fat high-energy diet with appropriate pancreatic enzyme supplements. Many patients are unable to achieve an adequate intake as a result of a variety of factors including chronic poor appetite, infection-related anorexia, gastro-oesophageal reflux and abdominal pain. Oral energy supplements and enteral tube feeding are widely used. Nutritional support has been shown to improve nutritional status and stabilise or slow the rate of decline in lung function. With such emphasis on nutritional intake and nutritional status throughout life, poor adherence to therapies and issues relating to body image are emerging. The median survival of patients with CF is increasing. CF is now considered a life-limiting disease of adulthood rather than a terminal childhood illness. With increased longevity new challenges are emerging that include the transition of young adults with CF to adult services, CF-related diabetes, disordered eating, osteoporosis, liver disease and transplantation.

Characteristics of adults with and without cystic fibrosis-related diabetes

AIMS

The prevalence of diabetes in adults with cystic fibrosis (CF) approximates 25%, yet few studies have defined risk factors. We examined the association between biochemical and clinical factors and CF-related diabetes.

METHODS

We performed a study in adults with CF in 2004 in Cambridgeshire, UK. Of 160 individuals, 51 had diabetes (cases) on the basis of medical history or screening using a 75-g oral glucose tolerance test, and 107 did not have diabetes (control subjects); two were excluded. We used logistic regression to model the cross-sectional association between potential risk factors and diabetes.

RESULTS

The mean age was 26 (16-58) years, mean body mass index (BMI) was 21 (16-28) kg/m(2), and mean forced expiratory volume in 1 s was 60 +/- 24% (mean +/- sd). All of the cases and 88% of control subjects had pancreatic insufficiency. Cases did not differ from control subjects with respect to age, sex, body mass index, or dose of oral pancreatic enzymes. Cases were more likely to have low serum magnesium, haemoglobin, and pulmonary function, and higher serum gamma-glutamyl transferase (GGT) activity, plasma fibrinogen levels, erythrocyte sedimentation rate, use of oral corticosteroids, and number of CF-related complications. In multivariate analyses, GGT, previous organ transplantation, plasma fibrinogen and the presence of CF-related complications were independently associated with diabetes, after controlling for corticosteroid use.

CONCLUSIONS

These data confirm the high prevalence of diabetes in adults with CF, and identify plasma fibrinogen and GGT, and organ transplantation as factors independently associated with CF-related diabetes. A prospective study would clarify the nature of these associations.