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Pneumocystis pneumonia

Last updated: January 8, 2021

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Pneumocystis jirovecii pneumonia (PCP), previously known as Pneumocystis carinii pneumonia, is an opportunistic fungal lung infection occurring almost exclusively in immunocompromised individuals. In 50% of cases, PCP is the first manifestation of AIDS (acquired immune deficiency syndrome), but it may be caused by other immunodeficiency disorders. PCP should be suspected in patients with a history of progressive dyspnea and a dry cough with resistance to standard antibiotic treatment. Signs that support this diagnosis include a CD4 count < 200/μL, an increased beta-D-glucan level, and diffuse bilateral infiltrates on chest x-ray. Management of PCP includes high-dose trimethoprim/sulfamethoxazole (TMP/SMX), treatment of the underlying immunodeficiency disorder, and steroids in the case of severe respiratory insufficiency.

A definitive diagnosis of PCP is not always possible. The following criteria should lead to a presumptive diagnosis of PCP:

The diagnosis should generally be confirmed via microscopic identification of P. jirovecii from respiratory secretions.

Clinical examination

PCP is often misdiagnosed as atypical pneumonia or bronchitis because of the persistent cough and similar auscultatory findings.

Laboratory tests


  • Chest x‑ray
    • Typically symmetrical, diffuse interstitial infiltrates extending from the perihilar region
    • May sometimes be normal
  • High-resolution CT
    • Indicated if PCP is still suspected in a patient with a normal CXR
    • High sensitivity for PCP (a negative scan thus suggests the diagnosis of PCP is unlikely)
    • Typical features
      • Ground-glass attenuation: symmetrical diffuse, interstitial infiltrates
      • Pneumatoceles: cystic air-filled spaces within the lung tissue

Acute infection [9]

If a patient with suspected PCP is acutely ill then empiric treatment should be started without delay.

PCP prophylaxis [9][11]

We list the most important complications. The selection is not exhaustive.

  • PCP was formerly the most common cause of death in HIV‑positive patients during the early years of the HIV epidemic. [2]
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  8. Goljan EF. Rapid Review Pathology. Elsevier Saunders ; 2013
  9. Maschmeyer G, Helweg-Larsen J, Pagano L, Robin C, Cordonnier C, Schellongowski P. ECIL guidelines for treatment of Pneumocystis jirovecii pneumonia in non-HIV-infected haematology patients. J Antimicrob Chemother. 2016; 71 (9): p.2405-2413. doi: 10.1093/jac/dkw158 . | Open in Read by QxMD
  10. Pentamidine. . Accessed: February 23, 2018.
  11. Guidelines for the prevention and treatment of opportunistic infections in HIV-infected adults and adolescents. Updated: October 18, 2017. Accessed: February 23, 2018.
  12. Bukhari H, Ayad M, Rosenthal A, Block M, Cortelli M. Superior vena cava syndrome secondary to thyroid cancer. J Surg Case Rep. 2011; 2011 (7): p.7. doi: 10.1093/jscr/2011.7.7 . | Open in Read by QxMD
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