Respiratory Bronchiolitis/Interstitial Lung Disease: Fibrosis, Pulmonary Function, and Evolving Concepts

Abstract

Abstract Context.—The concept of respiratory bronchiolitis/interstitial lung disease (RBILD) was introduced to explain the presence of interstitial lung disease in individuals whose only finding on surgical lung biopsy was smoker's respiratory bronchiolitis (RB). Over time, the diagnostic criteria for RBILD have become progressively more confused. Objective.—To review the diagnostic criteria for RBILD. Design.—The review was based on the literature and personal experience. Conclusions.—The concept of RBILD has changed over time with the recognition that, histologically and radiologically, RB and RBILD are usually indistinguishable. Most authors accept mild alveolar wall fibrosis extending away from the respiratory bronchioles as a part of both RB and RBILD, and occasional cases show quite marked, but probably localized, interstitial fibrosis. What has not been appreciated is that RB is not only an extremely common disease in cigarette smokers but also is ordinarily associated with airflow obstruction. Further, interstitial fibrosis is sometimes found in centrilobular emphysema, and this phenomenon has probably lead to some cases of centrilobular emphysema being misclassified as RB or RBILD. Despite the presence of fibrosis, centrilobular emphysema is still associated with airflow obstruction. We suggest that RBILD be restricted to the clinical setting in which cigarette smokers have a restrictive or mixed obstructive and restrictive functional abnormality, have a marked decrease in diffusing capacity with minimal evidence of airflow obstruction, or have imaging studies showing ground glass opacities/centrilobular nodules plus reticulation and no other lesion besides RB on biopsy to account for these changes. In this setting, the presence of RB-associated interstitial fibrosis probably causes the functional changes.