Expanded acceptance of acute exacerbation of nonspecific interstitial pneumonia, including 7 additional cases with detailed clinical pathologic correlation

: Acute exacerbation is uncommonly diagnosed in patients with nonspecific interstitial pneumonia (NSIP) and its pathologic features have received relatively little attention compared to idiopathic pulmonary fibrosis. We retrospectively studied 14 consecutive cases of histopathologically proven NSIP by surgical lung biopsy. The diagnosis of acute exacerbation was confirmed clinically. We analyzed whether four reported pathologic features, including organizing pneumonia lesion, alveolar hemorrhage, many fibroblastic foci, and focal hyaline membranes were present and suggestive of acute exacerbation of NSIP or not. Acute exacerbation in patients with NSIP was diagnosed in 8 cases, while the remaining 6 cases were diagnosed as clinically stable. Seven cases of organizing pneumonia lesion, 7 of alveolar hemorrhage, 6 of many fibroblastic foci, and 3 of focal hyaline membranes were identified as the main pathologic components in patients with acute exacerbation. Organizing pneumonia lesion and many fibroblastic foci were identified in 2 and 3 stable cases, respectively. Having more than two components was significantly associated with acute exacerbation. Evaluation of lung biopsies with NSIP for organizing pneumonia lesions, alveolar hemorrhage, many fibroblastic foci, and focal hyaline membranes may be useful to predict the possibility of acute exacerbation.