Abstract
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.
Highlights
Respiratory bronchiolitis-associated interstitial lung disease (RB-interstitial lung diseases (ILDs)) 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
Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD) has been incorporated into the broad category of diffuse parenchymal lung diseases that are known as the interstitial lung diseases (ILDs)
Within this large heterogeneous group of diseases, mostly of unknown etiology, respiratory bronchiolitis (RB)-ILD belongs to a subgroup termed idiopathic interstitial pneumonias (IIPs) [1,10]
Summary
Histologic features of surgical biopsy specimens According to the international consensus classification of the IIPs, the histopathologic diagnosis of RB-ILD requires the presence of brownish pigmented macrophages within respiratory bronchioles and alveolar ducts, associated with a patchy submucosal and peribronchiolar chronic infiltrate of lymphocytes and histiocytes (Figure 1). Other ILDs, including nonspecific interstitial pneumonia (NSIP) and subacute HP, should be taken into account in differential diagnosis These can be effectively excluded based on the HRCT findings: the ground-glass opacity observed in RB-ILD is usually patchier than that seen in NSIP or acute or subacute HP; a greater extent of micronodules in acute or subacute HP and the presence of diffuse bronchial wall thickening in RB-ILD may help in differentiating the two entities [14]. At follow-up HRCT after corticosteroid treatment and smoking cessation, the extent of bronchial wall thickening, centrilobular nodules, and ground-glass opacities had decreased in 43% of patients, while areas of hypoattenuation had increased as emphysema was irreversible on follow up [14]. In contrast to previous assumptions, RB-ILD is less commonly regarded as a benign entity
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