[1750] Histopathological Features of Acute Hypersensitivity Pneumonitis.

Lida P Hariri, Eugene J Mark, Maristela L Onozato, Yukako Yagi, Barry Shea, Subba Digumarthy, Armando Fraire, Osamu Matsubara, Mari Mino-Kenudsen. Massachusetts General Hospital, Boston; University of Massachusetts Memorial Medical Center, Worcester; National Defense Medical College, Tokorozawa, Japan

Background: Hypersensitivity pneumonitis (HP) is an interstitial disease which develops in response to antigen exposure, characterized by a bronchiolocentric chronic inflammatory response. Cases can be stratified by antigen load and exposure duration into acute, subacute, and chronic HP. While the pathologic features of subacute HP are established, those of chronic HP have only recently been described. No definitive pathological features of acute HP exist, because patients with acute presentation or rapid symptom resolution are infrequently biopsied.
Design: We evaluated 21 cases of clinically confirmed HP: 4 acute HP (acute, high-dose exposures without a background of subacute or chronic HP), 3 acute exacerbations in a background of subacute/chronic HP, 11 subacute HP, and 3 chronic HP. We semiquantitatively evaluated the bronchiolocentricity of chronic inflammation, loose histiocytic aggregates, giant cells, bronchiolitis obliterans, and organizing and/or fixed fibrosis. Interstitial inflammatory infiltrates were also evaluated (lymphocytes, plasma cells, eosinophils, and neutrophils). Fibrin content was assessed with phosphotungstic acid hematoxylin. Statistical comparisons were conducted using the Student's t-test.
Results: In acute HP and acute HP exacerbation, the extent of fibrin deposition was significantly greater (> 10% surface area with fibrin deposition/total area of disease) compared with subacute and chronic HP (p = 0.0016). Interstitial neutrophils were increased in the former (> 5 per HPF) when compared with the latter (p=0.0127). Fixed fibrosis was absent in all cases of acute HP, but was present in 1 of 3 cases of HP with acute exacerbation. One of the cases of acute HP had intraalveolar fibrin so marked it resembled acute fibrinous and organizing pneumonia. There was no statistically significant difference in the other characteristic features for HP between the 4 groups.

Conclusions: Fibrin greater than 10% in the area of inflamed lung and more than 5 neutrophils/HPF characterized acute HP or acute exacerbation of an underlying subacute or chronic HP. The finding of fibrin in these biopsies should raise suspicion for an acute antigen exposure.
Category: Pulmonary

Tuesday, March 1, 2011 2:30 PM

Platform Session: Section F, Tuesday Afternoon


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