Peribronchiolar Metaplasia: A Common Histologic Lesion in Diffuse Lung Disease and a Rare Cause of Interstitial Lung Disease

Abstract

Peribronchiolar metaplasia (PBM) is a histologic lesion consisting of peribronchiolar metaplasia (PBM) of bronchiolar-type epithelium. Although widely recognized, PBM has received little attention in the pathologic literature and is not known to have clinical significance. We identified 15 cases in which PBM was the only major histologic finding in surgical lung biopsies from patients with interstitial lung disease (PBM-ILD), and we reviewed the clinical, imaging, and pathologic findings. The mean age was 57 years (range, 44-74 years) with 13 females and 2 males. One patient had been a welder with fume and asbestos exposure; another had pigeon exposure. Smoking history was available for 13 patients: three current smokers, one cocaine user, two former smokers, and seven never smokers. Three patients had collagen vascular disease. One had elevated serum antinuclear antibody titers. Pulmonary function data were available for 10 patients: one obstructive, five restrictive, two mixed obstructive and restrictive, and two normal. Computerized tomography in 7 patients showed mosaic attenuation in 3 patients and air trapping in 1 patient; no bronchiectasis, septal lines, or honeycombing were seen in any cases. All 11 patients with available follow-up are alive; 4 of them have experienced symptomatic improvement (follow-up, 0.6-6.9 years; mean, 2.4 years). PBM was found focally in other interstitial lung diseases, which were assessed for this lesion: 59% of usual interstitial pneumonia (17 of 29), 50% of nonspecific interstitial pneumonia (10 of 20), desquamative interstitial pneumonia (3 of 6), hypersensitivity pneumonitis (9 of 18), and 11% of respiratory bronchiolitis (2 of 18). In summary, PBM is a common histologic finding in various interstitial lung disorders. It is rarely the sole major lung biopsy finding in patients presenting with interstitial lung disease (PBM-ILD). Patients are mostly older women, with mild symptoms and CT findings. Survival appears to be favorable.

Pathology of Chronic Hypersensitivity Pneumonitis What Is It? What Are the Diagnostic Criteria? Why Do We Care?

“…No CT imaging data were available. In contrast to isolated PBM, which generally appears to be innocuous, 34 3 of 9 patients (33%) with bronchiolocentric interstitial pneumonia and follow-up died of disease, and 5 others were alive with progressive disease. Yousem and Dacic 40 speculated that this process might be a form of CHP, but none of the cases had any obvious antigen exposures.…”

“…Moreover, PBM can be found in otherwise healthy lungs but is particularly frequently found in lungs with any kind of fibrosing interstitial pneumonias. Fukuoka et al 34 reported PBM in 17 of 29 UIP cases (59%), 10 of 20 NSIP cases (50%), 3 of 6 desquamative interstitial pneumonia cases (50%), 9 of 18 HP cases (50%), and 2 of 18 respiratory bronchiolitis with interstitial lung disease cases (11%). Myers and colleagues 29,35 concluded that PBM was present in 50% of HP biopsies and in 100% of HP autopsies but noted that the frequency of PBM was similarly high in UIP/IPF biopsies, so that it was not diagnostically useful in that context.…”

Hypersensitivity Pneumonia: Role of Surgical Lung Biopsy

“…Peribronchiolar lymphoid aggregates may be present and were seen in 79% of surgical lung biopsies reported by Trahan et al 37 Fibrosis of peribronchiolar interstitium may accompany the lymphocytic infiltrate and include hyperplasia of bronchiolar-type epithelium, a combination of histologic findings for which the term PBM has been proposed. 48 Peribronchiolar metaplasia is not specific, however, and may be seen in other conditions including UIP, NSIP, desquamative interstitial pneumonia, and a unique form of diffuse fibrotic airway disease termed PBM-interstitial lung disease or airway-centered interstitial fibrosis. 48,49 Peribronchiolar metaplasia is universal at autopsy in patients with chronic hypersensitivity pneumonia, but is also seen in nearly three-fourths of patients with UIP.…”

“…48 Peribronchiolar metaplasia is not specific, however, and may be seen in other conditions including UIP, NSIP, desquamative interstitial pneumonia, and a unique form of diffuse fibrotic airway disease termed PBM-interstitial lung disease or airway-centered interstitial fibrosis. 48,49 Peribronchiolar metaplasia is universal at autopsy in patients with chronic hypersensitivity pneumonia, but is also seen in nearly three-fourths of patients with UIP. 50 Other evidence of the bronchiolocentric nature of hypersensitivity pneumonia may include organizing pneumonia, referred to historically as bronchiolitis obliterans organizing pneumonia, which is present in as many as half of cases.…”

“…8,[34][35][36][37] As with UIP, important clues that should raise the possibility of hypersensitivity pneumonia include a bronchiolocentric distribution of the inflammation and/or fibrosis, PBM, and other evidence of small-airway injury such as organizing pneumonia and foamy alveolar macrophages in peribronchiolar air spaces. 8,37,48 Thus it is important to remain vigilant of the possibility even if all the classic findings are not seen.…”