Pathological characteristics for the diagnosis of Pneumocystis carinii pneumonia. A retrospective autopsy study

The clinical records of 63 patients who during the period 1980-1983 showed pneumocysts in lung specimen imprints obtained at autopsy have been reviewed in order to establish possible characteristics for the diagnosis of Pc pneumonia. Autopsies were performed at 2 Copenhagen hospitals, Rigshospitalet and the Finsen Institute. The 63 Pc-positive cases included 9 with blood diseases, 27 with solid tumors, 5 with immunological disorders and 22 with other diseases. The characteristic extensive changes in the lungs in Pc pneumonia included increased firmness, dark red/brown or black/grey colour of sectioned areas, stasis and edema sometimes excessive, and foci of white/grey or red/brown areas giving the lung a marbled or speckled appearance. The content of air was always decreased. The microscopic changes reported included intra-alveolar eosinophilic material, an intra-alveolar transudate containing macrophages and very few neutrophilic granulocytes, dilated capillary tubes, stasis and edema, thickened alveolar septae and peri-alveolar or diffuse fibrosis. The chest X-rays showed no specific features, and the infection had been subclinical in all cases; the only evidence of Pc infection was the demonstration of pneumocysts in imprints of lung specimens stained with toluidine blue in combination with observations during pathology. The diagnosis depends to a great extent upon a keen alertness in addition to the information given in the clinical record.