245.2 📚 國考版

245.2.0.1 必背 — Pathogen

  • Histoplasma capsulatum — dimorphic fungus
  • Mold (environment) ↔ yeast (37°C, intracellular in macrophages)
  • Small intracellular yeast (2-4 µm) on histology

245.2.0.2 必背 — Geography

  • USA endemic: Ohio + Mississippi River valleys
  • Also: Central + South America, Caribbean, Africa, Asia, Australia
  • Bird + bat droppings, caves, old buildings

245.2.0.3 必背 — Spectrum

  • Asymptomatic 90%
  • Acute pulmonary: flu-like, mostly self-limited; severe in heavy exposure
  • Chronic pulmonary: COPD/emphysema, cavitary (mimics TB)
  • Disseminated: HIV CD4 < 100 + immunocompromise; pancytopenia + multi-organ
  • Mediastinal forms (fibrosing severe complication)

245.2.0.4 必背 — Disseminated Clinical

  • Pancytopenia + hepatosplenomegaly + LAP + oral ulcers + adrenal insufficiency
  • HIV / immunocompromise
  • AIDS-defining

245.2.0.5 必背 — Diagnosis

  • Urinary Histoplasma Antigen (best for disseminated; 90% sens)
  • Serum antigen complementary
  • Antibody tests (chronic / mild)
  • Culture gold standard (slow)
  • Histology: small intracellular yeast in macrophages (GMS / Giemsa)
  • Elevated LDH + ferritin (disseminated)
  • Bone marrow biopsy high yield in disseminated

245.2.0.6 必背 — Treatment

Form Drug Duration
Asymptomatic / mild acute (immunocompetent) No treatment —
Acute pulmonary symptomatic Itraconazole 200 bid 6-12 wk
Severe acute pulmonary Liposomal AmB induction → itraconazole 1-2 wk + 12 wk
Chronic pulmonary Itraconazole 200 bid 12-24 mo
Disseminated mild Itraconazole 12 mo
Disseminated severe Liposomal AmB + itraconazole 1-2 wk + 12+ mo
HIV + disseminated Continue maintenance until CD4 > 150 × 6 mo on ART Variable
CNS Higher-dose AmB + itraconazole 12+ mo Long
Mediastinal forms Mostly supportive; antifungal limited Variable

245.2.0.7 必背 — Itraconazole TDM

  • Variable absorption, especially capsule
  • Take with food (solution preferred for absorption)
  • Trough > 1.0 mg/L target

245.2.0.8 必背 — HIV Specifics

  • CD4 < 100 + disseminated histoplasmosis = AIDS-defining
  • Treat aggressively + ART
  • Maintenance until CD4 > 150 × 6 mo on ART
  • Pre-emptive in some endemic areas

245.2.0.9 必背 — Differential

  • Tuberculosis (chronic pulmonary form mimics)
  • Sarcoidosis
  • Other dimorphic fungi (Blastomycosis, Coccidioidomycosis, Paracoccidioidomycosis)
  • Cancer
  • Lymphoma

245.2.0.10 必背 — Sclerosing / Fibrosing Mediastinitis

  • Rare severe complication of past infection
  • Late
  • Vascular + airway compression
  • Supportive primarily; antifungal limited

245.2.0.11 必背 — Adrenal Insufficiency

  • Common in disseminated
  • Bilateral adrenal masses
  • Steroid replacement
  • Often persists after treatment