Pneumocystis Infections

Pneumocystis pneumonia (PCP) is a form of pneumonia that is caused by the yeast-like fungus Pneumocystis jirovecii. It is also known as PJP, for Pneumocystis jiroveci Pneumonia.Chest X-ray of increased opacification (whiteness) in the lower lungs.These chest radiographs are of two patients. Both show ground glass opacities. The left X-ray shows a much more subtle ground-glass appearance while the right X-ray shows a much more gross ground-glass appearance mimicking pulmonary edema.X-ray of a cyst in pneumocystis pneumoniaHigh-resolution computed tomography (HRCT) showing ground-glass attenuation with a geographic or mosaic distribution.HRCT of cysts of pneumocystis pneumonia. These are usually multiple and bilateral, but range in size, shape and distribution. Pneumocystis pneumonia (PCP) is a form of pneumonia that is caused by the yeast-like fungus Pneumocystis jirovecii. It is also known as PJP, for Pneumocystis jiroveci Pneumonia. Pneumocystis pneumonia is not commonly found in the lungs of healthy people, but being a source of opportunistic infection, it can cause a lung infection in people with a weak immune system. PCP is especially seen in people with cancer undergoing chemotherapy, HIV/AIDS cases, and the use of medications that suppress the immune system. Signs and symptoms of PCP include fever, nonproductive cough (because sputum is too viscous to become productive), shortness of breath (especially on exertion), weight loss, and night sweats. Usually, not a large amount of sputum is produced with PCP unless the patient has an additional bacterial infection. The fungus can invade other visceral organs (such as the liver, spleen, and kidney), but only in a minority of cases. Pneumothorax is a well-known complication of PCP. An acute history of chest pain with breathlessness and diminished breath sounds is typical of pneumothorax. Also, a condition similar to acute respiratory distress syndrome (ARDS) may occur in patients with severe Pneumocystis pneumonia, and such individuals may require intubation. The risk of PCP increases when CD4-positive T-cell levels are less than 200 cells/μL. In these immunosuppressed individuals, the manifestations of the infection are highly variable. The disease attacks the interstitial, fibrous tissue of the lungs, with marked thickening of the alveolar septa and alveoli, leading to significant hypoxia, which can be fatal if not treated aggressively. In this situation, lactate dehydrogenase levels increase and gas exchange is compromised. Oxygen is less able to diffuse into the blood, leading to hypoxia, which along with high arterial carbon dioxide (CO2) levels, stimulates hyperventilatory effort, thereby causing dyspnea (breathlessness). The diagnosis can be confirmed by the characteristic appearance of the chest X-ray and an arterial oxygen level (PaO2) that is strikingly lower than would be expected from symptoms. Gallium 67 scans are also useful in the diagnosis. They are abnormal in about 90% of cases and are often positive before the chest X-ray becomes abnormal. Chest X-ray typically shows widespread pulmonary infiltrates. CT scan may show pulmonary cysts (not to be confused with the cyst-forms of the pathogen). The diagnosis can be definitively confirmed by histological identification of the causative organism in sputum or bronchoalveolar lavage (lung rinse). Staining with toluidine blue, silver stain, periodic acid-Schiff stain, or an immunofluorescence assay shows the characteristic cysts. The cysts resemble crushed ping-pong balls and are present in aggregates of two to eight (and not to be confused with Histoplasma or Cryptococcus, which typically do not form aggregates of spores or cells). A lung biopsy would show thickened alveolar septa with fluffy eosinophilic exudate in the alveoli. Both the thickened septa and the fluffy exudate contribute to dysfunctional diffusion capacity that is characteristic of this pneumonia. Pneumocystis infection can also be diagnosed by immunofluorescent or histochemical staining of the specimen, and more recently by molecular analysis of polymerase chain reaction products comparing DNA samples. Notably, simple molecular detection of P. jirovecii in lung fluids does not mean that a person has PCP or infection by HIV. The fungus appears to be present in healthy individuals in the general population.