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Pneumocystis jirovecii pneumonia

Reviewers: Elliot Weisenberg, M.D. (see Reviewers page)
Revised: 20 October 2014, last major update September 2011
Copyright: (c) 2003-2014, PathologyOutlines.com, Inc.

Clinical features

● Formerly known (incorrectly) as P. carinii, a pneumocystis variant that occurs in animals; P. jiroveci1 is specific to humans (eMedicine)
● Opportunistic yeast-like fungus present in bronchoalveolar lavage (BAL), sputum or biopsy
● Most common pneumonia in AIDS patients, who are at high risk if CD4 < 200 or if protein-calorie malnutrition
● May also occur in otherwise immunocompetent patients with protein-calorie malnutrition, hematologic malignancies or undergoing chemotherapy or chronic corticosteroid treatment
● Causes diffuse or patchy pneumonia; may have co-existing CMV or other infections
● Incidence has declined dramatically in HIV patients, but is increasing in other immunosuppressed patients, who have 24% mortality at 30 days (BMC Infect Dis 2011;11:76)
Radiology: usually atypical interstitial pneumonia; lung biopsy is rarely required for diagnosis


Life cycle


● Bronchoalveolar lavage and imprints have high sensitivity (Arch Pathol Lab Med 2007;131:1582)
● However, PCR plus expectorated or induced sputum is more cost-effective options than BAL or chest x-ray alone (PLoS One 2011;6:e23158)
● Also immunofluorescence


● Pentamidine, folic acid inhibitors (especially sulfonamides) and anti-HIV drugs
● Prophylactic therapy is currently routine in the setting of HIV and in combination with HAART treatment

Micro description

● Alveolar spaces filled with pink, foamy amorphous material composed of proliferating fungi and cell debris
● Fungi are 4-6 microns, cup/boat shaped cysts
● Also mild inflammatory reaction with fibrin exudate, hyaline membranes
● Solitary necrotizing granulomas and miliary disease are also described; granulomatous cases lack classic features of intra-alveolar foamy exudates with pneumocystis (Am J Surg Pathol 2010;34:730)

Micro images

Alveolar space with frothy material

Cup shaped organisms

GMS stain

Polychrome methylene blue stain

Fig 1: H&E and GMS inset; Fig 2 - pepsin pretreatment, hematoxylin only staining and polarized light; Fig 3 - GMS and polarized light

Various images

Positive stains

● GMS, Warthin Starry, other silver stains and Gram-Weigert

EM images

Alveolar space with frothy material

Differential Diagnosis

Alveolar proteinosis: diffuse pulmonary opacification and intra-alveolar PAS-positive material and lipid; exudative pulmonary edema, sputum contains gelatinous material; no inflammation; alveolar contents contain type II pneumocytes and necrotic alveolar macrophages
Goodpasture’s: necrotizing, hemorrhagic, interstitial pneumonitis; associated with rapidly proliferative glomerulonephritis, linear immunoglobulin deposits on basement membranes of alveolar septal walls; also intra-alveolar hemorrhage, septal thickening and hypertrophy, organization of blood in alveolar spaces
BOOP: bronchiolar and alveolar plugs of loose fibrous tissue

End of Lung-nontumor > Infections > Pneumocystis jirovecii pneumonia

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