246.1 🎓 醫孞生版

246.1.0.1 📌 䞀頁重點

246.1.0.1.1 Microbiology
  • Blastomyces dermatitidis (also B. gilchristii, B. helicus)
  • Dimorphic fungus (mold + yeast)
  • Tissue form: broad-based budding yeast (8-15 µm, thick refractile wall — pathognomonic)
246.1.0.1.2 Geography
  • Endemic USA: Mississippi + Ohio River valleys + Great Lakes (Wisconsin, Minnesota, Michigan, Ontario, Quebec — high)
  • Also: St. Lawrence basin, parts of Canada
  • Africa: sub-Saharan (B. dermatitidis + B. gilchristii)
  • Latin America, India sporadic
  • Soil + decaying organic matter near water
246.1.0.1.3 Transmission
  • Inhalation of conidia from environmental sources
  • Riverbanks, beaver dams, decaying wood
  • Outdoor activities (camping, hunting, gardening)
  • Outbreaks: shared exposure (point-source)
  • NOT person-to-person
246.1.0.1.4 Clinical (Less Common Than Histoplasmosis)
246.1.0.1.4.1 Asymptomatic (~ 50%)
246.1.0.1.4.2 Acute Pulmonary (Most Common Symptomatic)
  • 2-6 wk post-exposure
  • Flu-like → pneumonia
  • Productive cough, fever, weight loss
  • Severe: ARDS
246.1.0.1.4.3 Chronic Pulmonary
  • Months-years
  • Cavitary disease (mimics TB)
  • Lobar consolidation
246.1.0.1.4.4 Cutaneous
  • Verrucous (cauliflower-like) + ulcerative lesions
  • Face + hands + extensor surfaces
  • Often most striking clinical feature
  • Late lesion of disseminated disease
246.1.0.1.4.5 Osseous (10-15%)
  • Vertebra, ribs, skull, long bones
  • Lytic + sclerotic lesions
246.1.0.1.4.6 GU (Men > Women)
  • Prostatitis, epididymitis, orchitis
246.1.0.1.4.7 CNS (Rare but Severe)
  • Meningitis or cerebral abscess
  • High mortality
246.1.0.1.5 Diagnosis
  • Microscopy: broad-based budding yeast (sputum, pus, biopsy)
  • Culture (slow, definitive)
  • Blastomyces urinary antigen (sensitive 90%+ in moderate-severe; cross-reacts histoplasmosis)
  • Serology (less reliable; complement fixation, immunodiffusion)
  • PCR emerging
246.1.0.1.6 Treatment
  • Mild-Moderate pulmonary: Itraconazole 200 mg PO bid × 6-12 months (TDM > 1.0 mg/L)
  • Severe pulmonary / Disseminated / Immunocompromise: Liposomal Amphotericin B 3-5 mg/kg/d × 1-2 weeks → Itraconazole 200 mg bid × 12 months
  • CNS: Liposomal AmB 5 mg/kg/d × 4-6 weeks → Itraconazole 200 mg tid × 12+ months (some use voriconazole or fluconazole)
  • Pregnancy: AmB (azoles avoided)
246.1.0.1.7 Special
  • HIV + CD4 < 200: more severe disease
  • Acute respiratory distress (ARDS) in heavy exposure
  • Spectrum: from asymptomatic to fatal