Pleural plaques in smoking-associated fibrosis and pulmonary asbestosis

Abstract

Dear editor Bledsoe et al presents an interesting study examining the disparities between radiologic and pathologic diagnoses of asbestosis in cases referred for consultation in pulmonary malignancy.1 The authors conclude that the clinical diagnosis of asbestosis cannot be reliably distinguished from interstitial fibrosis in heavy smokers. These findings highlight the confounding role of cigarette smoking in the diagnosis of asbestosis when it is based on non-pathologic criteria. Clinical and radiographic characteristics of lung injury following particle exposure (including fibers in which one diameter of the particle is 3× that of the other by definition) are often comparable.2 The results of this investigation1 support further evaluation of a role for cigarette smoking in interstitial fibrosis. Furthermore, asbestos exposure can cause several non-malignant diseases of the pleura and lungs (ie, pleural effusions, pleural plaques, diffuse pleural fibrosis, rounded atelectasis, and asbestosis). Malignancies are also associated with asbestos exposure (ie, lung and laryngeal cancers and mesothelioma).3,4 Relationships between the dose–response and prevalence of asbestos-related diseases are complex.3,5 The injury requiring the least exposure, and which accordingly demonstrates the highest prevalence, is pleural plaque; 80% of individuals significantly exposed to asbestos (total dose of 0.1 fiber-year or less) will have plaques on the chest X-ray while only 0.5%–8% of an unexposed population will reveal such findings.6 Mesothelioma impacts 2,500 to 3,000 workers annually in the United States and its risk is elevated at a total asbestos dose of between 0.1 and 1.0 fiber-year. Those diseases requiring the greatest asbestos exposure are lung cancer and asbestosis; the risk for both is considered elevated at approximately 25 fiber-years. Bledsoe et al identify 24 cases with International Labour Organization (ILO) profusion score of ≥1, out of which only six cases show histological evidence of asbestosis. Of the remaining 18 cases, 16 are identified to have significant smoking history whereas two subjects had unknown smoking status. They observe radiographic evidence of pleural plaques in 82 (44%) of the cases included in the study. It would strengthen the conclusions of the study to know if those diagnosed with asbestosis demonstrated a higher prevalence of pleural plaques than those with cigarette smoking-related fibrosis.1