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Updated: Jul 26 2022

Pneumocystis jirovecii Pneumonia (PCP)

  • Snapshot
    • A 45-year-old woman presents to the clinic for a nonproductive cough of 2 weeks. She has been feeling increasingly fatigued, weak, and has had low-grade fevers. She reports that she also has shortness of breath with any physical exertion. She smokes 2 cigarettes a day. She has had 10 different sexual partners in the past month and does not use protection reliably. She has a past medical history of diabetes and reports that “something bad” was found on her labs a year ago but that she never followed-up as she had been feeling fine. On physical exam, she has diffused crackles in the lungs. Upon review of her chart, she had a positive HIV test a year ago. She is started on empiric antibiotics.
  • Introduction
    • Classification
      • Pneumocystis jirovecii pneumonia (previously Pneumocysis carinii pneumonia)
        • a yeast-like fungus
        • airborne transmission
    • Associated conditions
      • HIV
    • Prevention
      • smoking cessation
      • prophylaxis with medication
        • trimethoprim-sulfamethoxazole (TMP-SMX)
        • dapsone and pyrimethamine
  • Epidemiology
    • Incidence
      • decreased since the use of prophylaxis in vulnerable populations
      • more common in developing countries
    • Risk factors
      • immunodeficiency
      • HIV
      • malignancy
      • smoking
    • Pathogenesis
      • when both humoral and cellular immunity are suppressed, Pneumocystis attaches to the alveoli
      • activated alveolar macrophages without CD4+ cells are not able to fight the organisms
      • this causes hypoxemia with ↑ alveolar-arterial oxygen gradient and respiratory alkalosis
  • Presentation
    • Symptoms
      • most are asymptomatic in patients with normal immune systems
      • causes interstitial pneumonia in patients with immunosuppression
        • progressive exertional shortness of breath
        • chest pain
        • nonproductive cough
        • fever and chills
        • hemoptysis is rare
    • Physical exam
      • tachypnea, tachycardia, and fever
      • mild crackles and rhonchi in the bilateral lung fields
  • Imaging
    • Chest radiography
      • indication
        • all patients
      • findings
        • bilateral and diffuse infiltrates
    • Computed tomography (CT) of the chest
      • indication
        • if chest radiograph is unclear
      • findings
        • bilateral and diffuse patchy ground-glass opacities
        • pneumatoceles
  • Studies
    • Labs
      • ↑ lactic dehydrogenase
    • Pulmonary function tests
      • ↓ diffusion capacity of carbon monoxide < 75% predicted
      • high sensitivity
    • Histology
      • methenamine silver, Diff-Quik, or Wright stain of lung tissue
        • disc-shaped yeast
    • Making the diagnosis
      • based on lung biopsy or lavage and histology
      • lung tissue histology is needed for a definitive diagnosis
  • Differential
    • Cytomegalovirus (CMV) pneumonia
      • distinguishing factors
        • patients also present with pharyngitis as well as lymphadenopathy and splenomegaly
        • in HIV patients, CMV also involves the gastrointestinal tract
    • Tuberculosis
      • distinguishing factor
        • often presents with hemoptysis
  • Treatment
    • Management approach
      • treatment may be initiated prior to definitive diagnosis
    • Medical
      • trimethoprimsulfamethoxazole (TMP-SMX)
        • indications
          • first-line therapy
          • prophylaxis when CD4+ count < 200 cells/mm3
      • corticosteroids
        • indications
          • in HIV patients with severe cases (arterial-alveolar oxygen gradient > 35 mmHg or PaO2 < 70 mmHg)
          • always given alongside antibiotics
      • pentamidine
        • indication
          • second-line therapy if resistant to TMP-SMX
      • atovaquone
        • indication
          • second-line therapy if resistant to TMP-SMX
      • dapsone and pyrimethamine
        • indication
          • prophylaxis when CD4+ count < 200 cells/mm3
  • Complications
    • Acute respiratory distress syndrome
  • Prognosis
    • Mortality is 10-20%
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