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Histoplasma

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Summary

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Key Points

  • Histoplasma capsulatum
    • Characteristics
      • Dimorphic fungus
        • mold in soil
          • Have multicellular hyphae
        • yeast inside body (at body temperatures)
          • No hyphae seen in biopsy specimens
    • Transmission
      • Endemic to Mississippi and Ohio River Valleys
        • Found in bird or bat droppings (e.g. exploring caves, spelunking)
      • Inhalation of spores (MB)
      • Cannot be transmitted from person to person (unlike TB)
    • Presentation
      • Acute Histoplasmosis
        • Pneumonia
          • Patients who inhale a large inoculum of spores develop a severe and potentially fatal acute diffuse pulmonary infection
          • Usually lobular or acinar in distribution
          • CXR: normal or patchy infiltrates with hilar/mediastinal lymphadenopathy
          • Chronic infection can cause cavitations (resembles TB)
            • May form granulomas in mediastinal lymph nodes
        • Splenomegaly
        • Pancytopenia
        • Mouth ulcers
          • Seen in less than 10 percent of cases
          • Ulcerated lesions with heaped-up borders, resembling malignancy
      • Systemic dissemination
        • Rare, but seen in immunocompromised (e.g. HIV) and elderly
          • Itraconazole prophylaxis is given in AIDS with CD4 counts <150 cells/µL
        • CNS disease (e.g. meningitis)
        • Skin lesions
        • Pericarditis
        • Arthritis (joint pain)
        • Culture-negative endocarditis
    • Diagnosis
      • Histopathology
        • Granulomas are seen on biopsy
        • Macrophages filled with Histoplasma
          • Small ovoid fungi smaller than RBC
      • Fungal cultures
      • Histoplasma antigen detection in urine or blood
      • Fungal antibodies in serum
    • Treatment
      • Itraconazole for local infection
        • Fluconazole also used, but less active vs Histoplasma
      • Amphotericin B for systemic infection