Pathological differentiation of chronic hypersensitivity pneumonitis from idiopathic pulmonary fibrosis/usual interstitial pneumonia

Abstract

To evaluate the histological characteristics differentiating chronic hypersensitivity pneumonitis (chronic HP) with a usual interstitial pneumonia (UIP)-like pattern from idiopathic pulmonary fibrosis (IPF)/UIP. Surgical lung biopsy specimens from 22 patients with chronic HP diagnosed as having a UIP-like pattern upon histological examination and 13 patients with IPF/UIP were examined and the incidences of bronchiolitis, perilobular fibrosis, centrilobular fibrosis, bridging fibrosis, organizing pneumonia, fibroblastic foci, honeycombing, granulomas, giant cells, lymphocytic alveolitis and lymphoid follicles were compared. Bronchiolitis, centrilobular fibrosis, bridging fibrosis, organizing pneumonia, granulomas, giant cells and lymphocytic alveolitis were significantly more frequent among patients with chronic HP than among patients with IPF (all P<0.01). Centrilobular fibrosis, bridging fibrosis and organizing pneumonia, in addition to bronchiolitis, granulomas and giant cells, are characteristic features of chronic HP with a UIP-like pattern. These features are therefore important in differentiating chronic HP from IPF/UIP, as management strategies differ for the two disorders.