Pneumocystis carinii pneumonia: lung biopsy - a histopathologic study of typical and atypical features

The open and needle lung biopsies from 26 patients (12 males and 14 females), ranging in age from 5 mth to 60 yr (mean, 19 yr), with morphologically proven Pneumocystis carinii are retrospectively reviewed. A dry, nonproductive cough, fever, and tachypnea with bilateral interstitial alveolar infiltrates occurred rapidly in these patients with leukemia lymphoma (14), immunodeficiency states (5), metastatic carcinoma (3), lupus erythematosus (2), and renal transplants (2). When initially examining these biopsies at the time of frozen section the authors felt that many of them lacked the more typical or classic features, i.e., frothy intraalveolar exudates and lymphoplasmacytic infiltration of the interstitium. The presence or absence of these findings represents the basis on which a biopsy is classified as typical or atypical. Lymphocytes and histiocytes within the thickened alveolar septa, some forming into aggregates with a granulomatous appearance and a prominent intraalveolar macrophagic response, were noted in 1/3 of the biopsies. There was a tendency for this type of reaction to occur in patients with leukemia; however, none was in clinical relapse at the time pneumonia developed. Because of the marked variations in the histologic appearance, the pathologist should be cautious in his diagnosis at frozen section. Imprints of the tissue which are subsequently stained with methenamine silver are extremely helpful as a rapid diagnostic technique.