Respiratory bronchiolitis-interstitial lung disease.

Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD) is a rare, mild inflammatory pulmonary disorder that occurs almost exclusively in current or former heavy smokers, usually between the third and sixth decades, most likely with no gender predilection. The onset is usually insidious with exertional dyspnea and persistent cough, which may be non-productive, developing over a course of weeks or months. RB-ILD may also be diagnosed in asymptomatic patients with functional impairment and chest radiograph or high-resolution computed tomography (HRCT) abnormalities. Histologically, RB-ILD is characterized by the accumulation of yellow-brown pigmented macrophages within the lumens of respiratory bronchioles and alveolar ducts, associated with a patchy submucosal and peribronchiolar chronic inflammation. Common findings also include mild bronchiolar and peribronchiolar alveolar fibrosis that expands contiguous alveolar septa and leads to architectural distortion as well as centrilobular emphysema. Chest radiographs in patients with RB-ILD typically show fine reticulonodular interstitial opacities, while on HRCT central and peripheral bronchial wall thickening, centrilobular nodules, and ground-glass opacities associated with upper lobe centrilobular emphysema are most frequently reported. Pulmonary function testing may be normal but usually demonstrates mixed, predominantly obstructive abnormalities, often combined with hyperinflation and usually associated with a mild to moderate reduction in carbon monoxide diffusion capacity (DLco). The course of RB-ILD is heterogeneous. Some patients respond favorably to corticosteroids and/or smoking cessation, but often there is no functional improvement and the disease progresses despite smoking cessation and treatment.