Histopathologic analysis of sixteen autopsy cases of chronic hypersensitivity pneumonitis and comparison with idiopathic pulmonary fibrosis/usual interstitial pneumonia.

Hypersensitivity pneumonitis (HP) is an interstitial lung disease caused by the inhalation of organic substances and certain inorganic chemicals. The histopathologic features of chronic HP (CHP) have not been studied extensively. We examined the pathologic characteristics of 16 autopsy cases of clinically confirmed CHP and compared them with 11 cases of idiopathic pulmonary fibrosis/usual interstitial pneumonia (IPF/UIP). To clarify the exact intralobular location of the fibrotic lesions, we conducted 3-dimensional reconstruction of fibrosis of CHP and IPF/UIP. Granuloma was not detected in any CHP case. Similar to IPF/UIP, honeycombing lesions were found dominantly in the lower lobes in most CHP cases; upper lobe dominance and asymmetrical distribution of honeycomb lesions were more frequent in CHP than in IPF/UIP. In all lungs affected by CHP, centrilobular fibrosis was outstanding, often connecting to the perilobular areas in the appearance of "bridging fibrosis," which was clearly demonstrated by 3-dimensional imaging. Centrilobular and bridging fibrosis were significantly more conspicuous in CHP than IPF/UIP; however, considerable overlap was found. It is important to thoroughly explore the possibility of antigen exposure in cases of lungs with UIP with centrilobular fibrosis to discriminate CHP from IPF/UIP.