Granulomatous Pneumocystis carinii pneumonia mimicking tuberculosis

A 62-year-old man with untreated, well-differentiated lymphocytic lymphoma, presenting with progressive dyspnea, was found on open lung biopsy to have multiple necrotizing granulomas that on frozen section were initially called tuberculosis. Routine Grocott methenamine-silver stain showed these to contain Pneumocystis carinii organisms. A review of the literature shows that this is an unusual histologic presentation that can occur in a wide variety of immunosuppressed states, including the acquired immunodeficiency syndrome. The histologic similarities to tuberculous infection are stressed to increase the awareness of possible misdiagnosis that could result in delayed or inappropriate therapy.