Pneumocystis carinii infection in the acquired immune deficiency syndrome

The acquired immune deficiency syndrome (AIDS) pandemic has focused attention on Pneumocystis carinii pneumonia (PCP). Of special significance are the following key issues. (1) PCP in the AIDS patient can be clinically different than in the non-AIDS patient. (2) The morphologic expressions of PCP in both AIDS and non-AIDS patients are considerably more diverse than previously believed. (3) Rapid diagnostic methods that unequivocally demonstrate the PC microorganisms in the tissue and secretions are crucial to patient care. The clinical manifestations of PCP overlap with those of other pulmonary disorders so that its diagnosis requires at least bronchoscopy, if not an open lung biopsy. In biopsy specimens, typical and atypical histologic features allow the recognition of PCP under microscopic examination. The sensitivities of transbronchial biopsies and bronchoalveolar lavage are comparable, and their combination offers the greatest diagnostic yield. This article discusses the clinical and pathologic features of PCP in the AIDS patient, and explores the advantages and pitfalls of the various diagnostic methods for the identification of PC.