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Updated: Jul 22 2018

Pneumocystis jiroveci

  • Snapshot
    • A 32-year-old man with HIV presents to the clinic for increasing shortness of breath and a nonproductive cough for the past few days. He denies having any hemoptysis. On physical exam, he is found to be tachypneic and tachycardic, with diffuse crackles and rhonchi bilaterally. Laboratory exam reveals a lactic dehydrogenase of 300 U/L. A chest radiograph shows diffuse patchy infiltrates bilaterally. Empiric antibiotics are started immediately while a bronchoalveolar lavage is scheduled.
  • Introduction
    • Classification
      • Pneumocystis jirovecii pneumonia (previously Pneumocysis carinii pneumonia)
        • a yeast-like fungus
        • airborne transmission
    • 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
    • Associated conditions
      • HIV
    • Prevention
      • smoking cessation
      • prophylaxis with medication
        • trimethoprim-sulfamethoxazole (TMP-SMX)
        • dapsone and pyrimethamine
    • Prognosis
      • mortality is 10-20%
  • 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
      • trimethoprim-sulfamethoxazole (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
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