Granulomatous Pneumocystis carinii pneumonia complicating hematopoietic cell transplantation.

Pneumocystis carinii pneunonia (PCP) is associated with a wide spectrum of clinical and histopathological presentations. While granulomatous PCP uncommonly occurs in AIDS patients, it is extremely rare in other non-AIDS immunocompromised patients. We identified three patients who developed granulomatous PCP after bone marrow or blood stem cell transplantation. In all cases, fiberoptic bronchoscopy with bronchoalveolar lavage was non-diagnostic, and an open lung biopsy was required for diagnosis. All patients were successfully treated with trimethoprim-sulfamethoxazole. The histological appearance varied from an ill-defined granulomatous pneumonia to well-formed necrotizing granulomas. The typical intraalveolar eosinophilic frothy exudate was absent. Often sparsely distributed, the organisms were detected by GMS and immunohistochemical stains for P. carinii. No other pathogens were identified by additional histochemical stains or by microbiological cultures. Awareness of this unusual granulomatous tissue response to P. carinii and initiation of specific treatment can lead to successful resolution of this potentially lethal infection.