High-resolution CT in smoking-related interstitial lung diseases

In addition to chronic obstructive pulmonary disease (COPD) and bronchogenic carcinoma, smoking can also cause interstitial lung diseases (ILDs) such as respiratory bronchiolitis (RB), RB with ILD (RB-ILD), desquamative interstitial pneumonia (DIP), Langerhans cell granulomatosis (LCG) and idiopathic pulmonary fibrosis-usual interstitial pneumonia (IPF-UIP). However, smoking seems to have a protective effect against hypersensitivity pneumonitis (HP), sarcoidosis and organising pneumonia (OP). High-resolution computed tomography (HRCT) has a pivotal role in the differential diagnosis. RB is extremely frequent in smokers, and is considered a marker for smoking exposure. It has no clinical relevance in itself since most patients with RB are asymptomatic. It is frequent to observe the association of RB with other smoking-related diseases, such as LCG or pulmonary neoplasms. In RB-ILD, HRCT features are more conspicuous and diffuse than in RB, but there is no definite cut-off between the two entities and any distinction can only be made by integrating imaging and clinical data. RB, RB-ILD and DIP may represent different degrees of the same pathological process, consisting in a bronchiolar and alveolar inflammatory reaction to smoking. Smoking is also a well-known risk factor for pulmonary fibrosis. Multidisciplinary discussion and follow-up can generally solve even the most difficult cases.