Rapid Fall in Lung Density Following Smoking Cessation in COPD

Introduction: Whether smoking-induced lung inflammation subsides after smoking cessation is currently a matter of debate. We used computed tomography (CT) to evaluate the effect of smoking cessation on lung density in patients with COPD. Material and methods: Thirty-six patients quit smoking out of 254 current smokers with COPD who were followed with annual CT and lung function tests (LFT) for 2-4 years as part of a randomised placebo-controlled trial of the effect of inhaled budesonide on CT-lung density. Lung density was expressed as the 15th percentile density (PD15) and relative area of emphysema below -910 HU (RA-910). From the time-trends in the budesonide and placebo groups the expected CT-lung densities at the first visit after smoking cessation were calculated by linear regression and compared to the observed densities. Results: Following smoking cessation RA-910 increased by 2.6% (p = 0.003) and PD15 decreased by -4.9 HU (p = 0.0002). Furthermore, changes were larger in the budesonide group than the placebo group (PD15: -7.1 vs -2.8 HU. RA-910 3.7% vs 1.7%). These differences were, however, not statistically significant. The LFT parameters (FEV1 and diffusion capacity) were not significantly influenced by smoking cessation. Conclusion: Inflammation partly masks the presence of emphysema on CT and smoking cessation results in a paradoxical fall in lung density, which resembles rapid progression of emphysema. This fall in density is probably due to an anti-inflammatory effect of smoking cessation.