Pathologic features of smoking-related lung diseases, with emphasis on smoking-related interstitial fibrosis and a consideration of differential diagnoses.

Smoking-related interstitial fibrosis (SRIF) is frequently-seen and morphologically-distinctive finding in the lung tissue of cigarette smokers. It can be distinguished histologically from the idiopathic interstitial pneumonias and other causes of pulmonary interstitial fibrosis. SRIF is typified by dense thickening of the alveolar septa by thick collagen bundles with a hyalinized appearance, with the common admixture of bands of hyperplastic smooth muscle. Concomitant inflammation is minimal. SRIF predominates in the subpleural and centrilobular parenchyma, and is usually accompanied by the changes of centrilobular emphysema and respiratory bronchiolitis. Most patients with SRIF do not have clinical symptoms of the condition. This article reviews the pathologic features of SRIF and compares them with the appearances of other interstitial lung diseases, some of which are also related to cigarette smoking. Acute eosinophilic pneumonia is another lung disease that has an association with smoking, and its clinicopathologic features are considered here as well.