Respiratory bronchiolitis-associated interstitial lung disease.

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).