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PubMed search: Pneumocystis jirovecii [title] pneumonia pulmonary

Elliot Weisenberg, M.D.
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Cite this page: Weisenberg E. Pneumocystis. website. Accessed September 22nd, 2023.
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 coexisting 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
Diagrams / tables

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Life cycle

Life cycle

  • 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
Microscopic (histologic) 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)
Microscopic (histologic) images

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Cup shaped organisms

Cup shaped organisms

GMS stain GMS stain

GMS stain

Polychrome methylene blue stain

Polychrome methylene blue stain

Positive stains
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 syndrome: 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
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