Spectrum of pathologic manifestations of Pneumocystis carinii pneumonia in patients with neoplastic diseases.

Abstract

Pneumocystis carinii is the most common protozoan organism causing infection in immunosuppressed patients. This study, based on a review of 32 lung biopsies and 13 autopsies of patients with neoplastic diseases who developed P carinii pneumonia, emphasizes the morphologic variation of this disease. Excluded from this study are those patients with PCP secondary to bone marrow transplantation and AIDS. P carinii pneumonia occurred predominately in patients with malignant lymphoreticular neoplasms, 73% of those in our series, and the remaining 27% had solid tumors. There were 27 males and 18 females and their ages ranged from 1 to 73 years, with a median age of 30 years. Microscopically, the diagnostic intraalveolar foamy exudate of P carinii pneumonia was present in only 58% of the cases. Furthermore, diffuse alveolar damage alone was present in 26% of cases. This change was especially prominent when the characteristic foamy material was scanty. Other tissue reactions to P carinii included the presence of giant cells, epithelioid granulomas, desquamative interstitial-like pneumonitis, and interstitial lymphoid infiltrate. Extrapulmonary dissemination was not observed in this patient population. The pathologist should be aware of the marked variations that occur in the morphologic appearance of PCP, and the diagnosis of Pneumocystis infection should not be discarded until a careful search for the organisms using silver stains is rendered negative.