The pathology of treated Pneumocystis carinii pneumonia.

Post-mortem examinations were conducted in 28 patients with the acquired immune deficiency syndrome (AIDS) and biopsy-proven Pneumocystis carinii pneumonia (PCP) who had been treated with trimethoprim-sulfamethoxazole (Bactrim, intravenous infusion [Roche]) and/or pentamidine isethionate. According to the evolution of the pulmonary process, the cases were classified into three groups. Group I ("fulminant" PCP) was composed of eight patients who died during the first week of the disease. Although treatment had eradicated most of the organisms, one third of the alveolar space volume, on the average, was filled by foamy exudates characteristic of PCP. This accounted for the respiratory insufficiency and death of these patients. Group II ("nonresolving" PCP) was comprised of nine patients who died within eight days and 2 months of diagnosis. PCP was less severe than in group I, but fatal respiratory insufficiency was the result of fibroblastic organization of the intraalveolar exudates (fibrosing alveolitis). In seven of the nine patients (78%), the latter resulted from oxygen toxicity; in the remaining two patients (22%) PCP, per se, was the original stimulus for the fibrosis. Patients in group II also had a high incidence of thromboembolic pulmonary lesions. Group III ("cured" PCP) was composed of 11 patients who responded dramatically well to therapy but died months or years later of other manifestations of AIDS. In group III patients, the roentgenographic picture at diagnosis was consistently less severe than in groups I and II.