A Review of Respiratory Bronchiolitis and Respiratory Bronchiolitis-Associated Interstitial Lung Disease

Abstract

Respiratory bronchiolitis (RB) and respiratory bronchiolitis-associated interstitial lung disease (RB-ILD) are 2 processes that lie along the continuum of probable smoking related lung diseases. The separation of the 2 is difficult and sometimes contentious; however, the combination of clinical symptoms and suggestive pathologic findings usually allows for a distinction and the subsequent diagnosis.RB in an asymptomatic smoker is considered an incidental histologic finding consistent with prior tobacco history. RB-ILD, although histopathologically similar to RB, is characterized by more extensive pulmonary parenchymal involvement and clinical expression as defined by dyspnea or other respiratory complaints. On pulmonary function testing, RB-ILD patients often demonstrate a mixed picture of obstructive or restrictive physiology, in combination with a reduced carbon monoxide diffusion capacity. Plain chest radiography is of limited utility and can be normal in many RB-ILD patients. High-resolution computer-assisted tomography scanning in the setting of RB-ILD correlates with the extent of bronchiolitis on pathologic analysis and offers a potential role for assessing response to therapy. Thus far, bronchoscopy has demonstrated a relatively limited capacity in diagnosing RB-ILD, necessitating surgical lung biopsy to arrive at a definitive diagnosis. Treatment of RB-ILD hinges upon smoking cessation maneuvers and consideration of immunosuppressive agents in recalcitrant cases.Key Words: respiratory bronchiolitis, interstitial lung disease, kaolinite (Clin Pulm Med 2004;11: 219 -227) S moking has been associated with a variety of pathologic findings, all of which have an equally varied clinical expression as disease processes. Additionally, the acceptance that only a relatively small percentage of smokers will potentially develop a tobacco-related pulmonary process suggests a complex interaction between environment, genetic predisposition, lifetime tobacco burden, and pulmonary pathology. It is not surprising that pathologic markers of smoking such as respiratory bronchiolitis (RB) and RB-associated interstitial lung disease (RB-ILD) should also assume a spectrum of presentations. In asymptomatic individuals, RB is considered to be a histologic marker of inhaled tobacco particulates. As opposed to RB, RB-ILD is a clinical syndrome associated with a potentially disabling symptom complex. Epidemiology of RB and Peribronchiolar Inflammation/FibrosisNiewoehner et al 1 in 1974 were one of the first groups to provide insight into the histologic changes at the bronchiolar level which may ensue from tobacco use. They performed autopsies on 39 patients who died of extrapulmonary causes. Lung specimens from 24 of the patients demonstrated yellowbrown pigmented macrophage accumulation within the respiratory bronchioles and juxtaposed airspaces with minimal peribronchiolar inflammation. Nineteen of the 24 patients with peribronchiolar inflammation had a history of smoking. The finding of peribronchiolar pigmented macrophage acc...