Histopathologic Analysis of Sixteen Autopsy Cases of Chronic Hypersensitivity Pneumonitis and Comparison With Idiopathic Pulmonary Fibrosis/Usual Interstitial Pneumonia

Abstract

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.

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

“…Most of the information on separation of UIP/IPF from CHP is derived from qualitative statements in the literature, but Akashi et al 31 and Takemura et al 26 …”

“…Bridging fibrosis is common in CHP ( Table 2), and some authors suggest it is a prototypical lesion that is rarely seen in UIP. 26,30,31 A UIP-like pattern, with patchy, subpleural fibrosis; fibroblast foci; and some amount of microscopic honeycombing, is also common in CHP (Figure 2, C), but often, the pattern in CHP is subtly different from UIP/IPF, with relatively less subpleural fibrosis, little to no honeycombing, and sometimes fibrosis that follows alveolar walls immediately under the pleura, rather than forming the large solid blocks of fibrosis typical of UIP/IPF (Figures 2, A, and 3). As well, the degree of peribronchiolar fibrosis or bridging fibrosis may be as severe as, or worse than, the subpleural fibrosis (Figures 2, A, and 3).…”

Hypersensitivity Pneumonia: Role of Surgical Lung Biopsy

“…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. Prominent foamy macrophage within peribronchiolar alveolar spaces (ie, microscopic obstructive pneumonia) is another finding that frequently attests to the presence of bronchiolitis and physiologic airflow obstruction in patients with hypersensitivity pneumonia.…”

“…8,34,36,37,50 Indeed, in some patients with late stage disease it may become nearly impossible to distinguish idiopathic pulmonary fibrosis from chronic hypersensitivity pneumonia, but at this stage the distinction may have little impact on outcome as both have the same poor prognosis. 32,34 In other patients the distinction hinges on identifying areas away from the fibrosis that demonstrate the classic combination of a cellular, bronchiolocentric, lymphocyte-rich, interstitial infiltrate with the characteristic pattern of associated granulomatous inflammation.…”

“…6,37 Prominent PBM, although not specific, is more common and tends to be more extensive in chronic hypersensitivity pneumonia compared with UIP. 50 In an otherwise typical case of UIP, pronounced PBM should trigger a careful search for the findings more characteristic of classic chronic hypersensitivity pneumonia. Upper lobe predominance of honeycomb change, something likely to be more easily appreciated on HRCT than surgical lung biopsy, can serve as another clue to a diagnosis of chronic hypersensitivity pneumonia.…”