Cigarette smoking contributes to idiopathic pulmonary fibrosis associated with emphysema

Background Combined emphysema and pulmonary fibrosis, including idiopathic pulmonary fibrosis (IPF), is a distinct disorder described with upper-lobe emphysema and lower-lobe fibrosis on chest computed tomography. Smoking appears to be the predominant risk factor for this disorder. We aimed to compare clinical features, smoking history, physiological and radiological findings between IPF with and without emphysema. Methods A sample of 125 IPF patients over a period of 48 months were evaluated. High resolution CT scans were reviewed blinded to clinical data. The IPF patients with or without emphysema were classified accordingly. Results The prevalence of emphysema in this IPF sample was 70/125. IPF with emphysema was significantly associated with smoking status (OR 63; 95% CI 4.4 to 915; P=0.002) and smoking pack year (OR 1.1; 95% CI 1.05 to 1.13; P=0.000). The patients with IPF and emphysema had a higher decrease in carbon monoxide diffusing capacity adjusted for alveolar volume ((58±19)% pred vs. (66±21)% pred; P=0.021) and a higher prevalence of pulmonary hypertension (24/70 vs. 7/55; P=0.006). The two groups of patients had similar forced and residual volumes. No significant differences were found in cell differentials of bronchoalveolar lavage or the scores of fibrosis on chest CT. Survival of the patients with emphysema was significantly less than that of patients with IPF alone. Conclusions Cigarette smoking induces IPF combined with emphysema. Emphysema further impairs physiological function and increases the prevalence of pulmonary hypertension that leads to poor prognosis. The inclusion of the patients with combined pulmonary fibrosis and emphysema in IPF clinical trials may lead to under evaluation of the effect of treatment in patients.