Respiratory Bronchiolitis-Associated Interstitial Lung Disease

Athol U. Wells, M.D.; Andrew G. Nicholson, D.M.; David M. Hansell, M.D.; Roland M. du Bois, M.D.

Disclosures

Semin Respir Crit Care Med. 2003;24(5) 

In This Article

Abstract and Introduction

Abstract

Respiratory bronchiolitis-associated interstitial lung disease (RBILD) can be viewed as an exaggerated respiratory bronchiolitic response to cigarette smoke. The histologic, high-resolution computed tomographic (HRCT) and bronchoalveolar lavage (BAL) features of RBILD overlap substantially with those of respiratory bronchiolitis, with the diagnosis of RBILD being based upon the severity of disease, as judged by symptoms, clinical signs, the severity of lung function impairment, and the extent of abnormalities on HRCT. Typical histologic appearances consist of an accumulation of pigmented macrophages within respiratory bronchioles, associated with peribronchial chronic inflammatory cell infiltration and, variably, peribronchial fibrotic alveolar septal thickening. Characteristic HRCT findings include poorly defined centrilobular micronodules, patchy limited ground-glass attenuation, bronchial wall thickening, and areas of regional hypoattenuation. The ventilatory defect is often mixed but is usually predominantly restrictive. The diagnosis of RBILD is often made on clinical and HRCT criteria, with BAL findings providing useful diagnostic support, but a thoracoscopic biopsy continues to be required when other features are atypical. RBILD may regress with discontinuation of smoking but often persists with no functional improvement despite smoking cessation and treatment. Nonetheless, the course tends to be benign, without inexorable deterioration. This article outlines the rationale for viewing RBILD and desquamative interstitial pneumonia as separate entities, rather than two ends of the same disease spectrum (based upon overlapping histologic and HRCT features).

Introduction

Respiratory bronchiolitis-associated interstitial lung disease (RBILD) is a clinically overt, smoking-related, interstitial lung disease in which the essential histologic features are indistinguishable from smoking-related respiratory bronchiolitis. Thus, the diagnosis of RBILD is essentially clinical, requiring the presence of a variable combination of symptoms, clinical signs, pulmonary function abnormalities, and abnormal findings on chest radiography or high-resolution computed tomography (HRCT). However, despite numerous clinical descriptions, there is no universal agreement on the exact clinical distinction between RBILD and respiratory bronchiolitis. In particular, it is likely that the same HRCT and histologic abnormalities are variably classified as respiratory bronchiolitis and RBILD in different series. The level of pulmonary function impairment is not always a reliable discriminator between respiratory bronchiolitis and RBILD because it may be confounded by other smoking-induced pathologic disorders, especially emphysema. In view of the major overlap between these disorders, respiratory bronchiolitis and RBILD are discussed and contrasted in this review. Distinctions between RBILD and desquamative interstitial pneumonia (DIP) are also highlighted; although histologically distinct, the two patterns have features in common and are viewed by some as ends of a spectrum of the same smoking-related disease process, rather than as separate entities.

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