Nonspecific interstitial pneumonia/fibrosis. Histologic features and clinical significance.

Sixty-four cases of interstitial pneumonia were identified that could not be classified into one of three main categories of idiopathic interstitial pneumonia. These cases, descriptively termed nonspecific interstitial pneumonia/fibrosis, were characterized by varying proportions of interstitial inflammation and fibrosis that appeared to be occurring over a single time span (i.e., the process was temporally uniform.) The most common presenting complaint was dyspnea for several months, and chest radiographs usually showed bilateral interstitial infiltrates. The prognosis was good with only five deaths due to progressive respiratory disease in 48 patients with known follow-up (11%). No deaths occurred in patients whose biopsies showed pure inflammation and no fibrosis. Nonspecific interstitial pneumonia must be separated from the three main forms of idiopathic interstitial pneumonia because of better prognosis and different treatment options. It should not be considered a specific disease, however, because it may have varying etiologies including underlying connective tissue diseases, organic dust or other exposures, and prior acute lung injury; less often, it may reflect a nonrepresentative biopsy of another process.