The pathological manifestations of pulmonary toxoplasmosis in the acquired immunodeficiency syndrome.

Pulmonary toxoplasmosis, once considered a rare complication of human immunodeficiency virus infection, recently has been reported with increasing frequency in patients with the acquired immunodeficiency syndrome (AIDS). However, published descriptions of the pathologic changes have been scanty, involve mainly single cases, and appear to conflict. Four cases of pulmonary toxoplasmosis observed at autopsy in patients with AIDS were reviewed. Two of the patients presented with Toxoplasma pneumonia and in one the diagnosis was made antemortem by open lung biopsy. Two patterns of pulmonary lesions associated with Toxoplasma gondii pneumonia were identified and appeared to be related to the stage and intensity of the infection. A pattern of interstitial pneumonitis/diffuse alveolar damage with a fibrinous alveolar exudate appeared to antecede a necrotizing pneumonia characterized by large areas of parenchymal necrosis. In the former pattern T gondii tachyzoites were found in small numbers and were mainly intracellular, whereas in necrotic areas tachyzoites were numerous and were extracellular as well as intracellular. Histopathologic diagnosis of the infection required careful search for the organisms even when they were plentiful Immunohistochemistry identified far more organisms than could be appreciated with routine stains and confirmed the diagnosis.