The role of lung diffusing capacity for carbon monoxide in Pulmonary Langerhans Cell Histiocytosis

<bold>Introduction</bold> Diffusing capacity of the lung for carbon monoxide (DLCO) measures the efficiency of the alveolar-capillary membrane to exchange respiratory gases (O2 and CO2) between the alveoli and lung capillaries. <bold>Material and methods</bold> In this single-centre observational study, data from 54 patients with a histological diagnosis of PLCH were assessed. In addition to gender, age and smoking history, patients were stratified into four CT patterns: nodular, cystic, nodular-cystic and fibrotic-cystic. <bold>Results</bold> Mean z-score of DLCO,KCO and ΔDLCO (the difference between the first and the 1-year DLCO measurement [ΔDLCO]) for women were similar to men. A significant negative correlation was observed between mean number of pack years and the mean percentage of predicted DLCO (r= −0.35; p= 0.009) and between mean number of pack years and mean z-score of DLCO (r= −0.39; p= 0.003). The mean z-score of DLCO in nodular pattern (0.2 + 1.7) was significantly higher than the nodular-cystic pattern (−1.5 + 2.6) and fibrotic-cystic pattern (−2.5 + 1.9) (p= 0.04 and p= 0.01, respectively). The mean z-score of KCO in nodular pattern (0.07 + 1.36) was higher than fibrotic-cystic pattern (−2.1 + 2.5) (p=0.025). <bold>Conclusion</bold> The correlation between the mean number of pack years and DLCO showed that heavy smokers are at greater risk of developing a low DLCO. We also found that nodular-cystic and fibrotic-cystic patterns were associated with lower DLCO (z score) and KCO (z score). In conclusion, this observational study shows that at diagnosis, older heavy smokers with a nodular-cystic or fibrotic-cystic CT pattern at diagnosis, are at higher risk of having lower DLCO and/or KCO.