Is the Histologic Finding of Smoking-Related Interstitial Fibrosis (SRIF) Specific for Smoking? Histologic Analysis of 600 Surgical Lung Specimens from Current Smokers, Ex-smokers and Never-Smokers

Abstract Respiratory bronchiolitis (RB) and emphysema are histologic manifestations of cigarette smoking in lung parenchyma. In 2010, a histologic finding known as smoking-related interstitial fibrosis (SRIF) was described in smokers. We undertook this study to determine the specificity of SRIF as a histologic marker of smoking. An H&E-stained slide representative of non-neoplastic lung was selected from 600 consecutive surgically resected lung specimens and assessed for RB, emphysema and SRIF by a pulmonary pathologist blinded to smoking status. Smoking status was retrieved from medical records by another pathologist. The specificity of each histologic finding for smoking status was calculated. There were 600 lungs from 600 patients (309 men, 291 women; mean age 62y, range 6–91) including 444 smokers (88 current, 356 ex) and 156 never-smokers. Sixty-eight cases with SRIF (68/600, 11%) were diagnosed by the pathologist blinded to smoking status; in all 68, the patient was a smoker (current smokers 25; ex-smokers 43; 34 men/34 women, mean age 63y, range 33-82y) with a mean of 46.7 pack-years of smoking (range 7.5-122.5 pack years). Of 139 cases with RB alone, 98 were smokers and 41 were never-smokers. Of 43 patients with emphysema alone, 34 were smokers and 9 were never-smokers. Of 197 cases with RB plus emphysema, 173 were smokers and 24 were never-smokers. The specificity of SRIF for smokers (100%) was higher than RB alone (74%), emphysema alone (94%), and RB plus emphysema (85%). SRIF occurs exclusively in cigarette smokers, and is a more specific smoking-related histologic finding than RB or emphysema.