Pneumocystis pneumonia

OVERVIEW

• Pneumocystis pneumonia: form of pneumonia caused by the yeast-like fungus Pneumocystis jirovecii, most commonly as an opportunistic infection in the immunosuppressed
• the classical presentation is pneumonia in the immunosuppressed and it is an AIDS-defining illness in HIV patients
• PCP is still an acceptable term (PneumoCystis Pneumonia) though PJP is now commonly used as an abbreviation

CAUSE

Pneumocystis pneumonia is caused by P. jirovecii

• P. jirovecii was previously thought to be P. carinii (a species that actually infects rats!)
• reclassified as a ‘yeast-like’ fungus on the basis of nucleic acid and biochemical features
• Pneumocystis spp. cannot be cultured

CLINICAL FEATURES

History

• subtle onset of progressive dyspnea, nonproductive cough, and low-grade fever
• abrupt onset of respiratory insufficiency that may correlate with a tapered or increased dosage of immunosuppressant medications in non-AIDS patients
• history of immunosuppression (e.g. HIV/AIDS, SLE, organ transplantation, immunosuppressants)
• sudden onset chest pain and dyspnea suggests pneumothorax

Exam

• tachypnea
• tachycardia
• signs of pneumothorax
• lung exam usually unremarkable

INVESTIGATIONS

• Induced sputum or BAL
  • Giemsa and methenamine silver stains (for microscopic visualization of characteristic cystic or trophic forms in respiratory specimens)
  • PCR (highly sensitive, detects colonisation as well  as infection)
• Test for HIV and CMV (co-infection is common)
• Consider other causes of immune-suppression (e.g. PCP in the context of a new severe presentation of SLE)
• CXR: bilateral, symmetric, reticular (interstitial), or granular opacities; pneumatoceles; pneumothorax (may be bilateral)
• HRCT Chest: ground glass opacities (must be present)

MANAGEMENT

Specific therapy

• co-trimoxazole (trimethoprim 20mg/kg/day and sulphamethoxazole 150mg/kg/day in 4 divided doses) for 21 days (IV; PO for mild cases)
• Second line:
  • pentamidine or
  • trimethoprim + dapsone or
  • clindamycin + primaquine or
  • atovaquone
• Steroids should be used in patients with HIV and significant hypoxaemia (PaO2 <70 mmHg or A-a gradient >35 mmHg)
  • e.g. prednisolone 40m bd for 5 days, then taper over 21 days total
  • long term prophylaxis (see below)

Pneumothorax may require long-term chest drains

PROGNOSIS

• 10-20% mortality for initial PCP infection in AIDS patients; much higher if requiring mechanical ventilation
• 30-60% mortality for initial PCP infection in patients without AIDS

PROPHYLAXIS

Primary prophylaxis against PCP should be given if:

• HIV positive and CD4+ count is less than 200 cells per millimeter
• HIV positive and history of oropharyngeal candidiasis

Secondary prophylaxis is lifelong unless there is IRIS from HAART (i.e. CD4 >200)

References and Links

LITFL

• CCC — HIV and AIDS

Journal articles

• Huang L, et al; International HIV-associated Opportunistic Pneumonias (IHOP) Study; Lung HIV Study. HIV-associated Pneumocystis pneumonia. Proc Am Thorac Soc. 2011 Jun;8(3):294-300. PMC3132788.
• Krajicek BJ, Thomas CF, Limper AH. Pneumocystis pneumonia: current concepts in pathogenesis, diagnosis, and treatment. Clinics in chest medicine. 30(2):265-78, vi. 2009. [pubmed]
• Thomas CF Jr, Limper AH. Pneumocystis pneumonia. N Engl J Med. 2004 Jun 10;350(24):2487-98. Review. PMID: 15190141pneumatoceles

FOAM and web resources

• Radiopaedia — Pneumocystis pneumonia