OBJECTIVETo study the clinicopathologic features and diagnostic approach of chronic extrinsic allergic alveolitis (EAA).

METHODSSeven cases of chronic EAA diagnosed by open lung biopsy or lung transplant were enrolled into the study. The clinical and pathologic features were analyzed and the literature was reviewed.

RESULTSThere were altogether 4 men and 3 women. The age of the patients ranged from 30 to 65 years (mean = 48 years). All cases represented chronic form and five cases diagnosed by open lung biopsy also showed features of recent aggravation, leading to hospitalization. Four cases had known history of exposure to inciting gases, pollens and pets, and only 2 cases were positive for allergens. High-resolution CT scan showed ground-glass attenuation and reticular pattern that often had a patchy distribution and central predominance. Bronchoalveolar lavage analysis showed marked lymphocytosis, with CD4(+)/CD8(+) ratio less than 1. Lung function test demonstrated a restrictive ventilatory defect, with decreased compliance, reduced diffusion capacity and high airway obstruction. Five cases had open lung biopsy performed and two cases had undergone lung transplantation. Pathologic examination showed bronchiolocentric cellular interstitial pneumonia, interstitial fibrosis, non-caseating epithelioid granulomas, epithelioid histiocytic infiltrate in the respiratory bronchioles and intraluminal budding fibrosis. The five cases with open lung biopsy performed also showed neutrophilic infiltrate in the alveoli. The two lung transplant cases were complicated by severe fibrotic changes.

CONCLUSIONSChronic EAA demonstrates characteristic pathologic features. Definitive diagnosis requires correlation with clinical and radiologic findings due to possible morphologic mimicry of other diffuse parenchymal lung diseases.