Morphology: Dimorphic fungus — mold in soil; yeast (8–15 μm, broad-based budding, refractile double-contoured wall) in tissue at 37°C.
Dimorphic
Typical drugs
- #1Itraconazole— Mild–moderate pulmonary and step-down (≥6–12 mo).
- #2Amphotericin B (liposomal)— Severe pulmonary, CNS, immunocompromised — induction × 1–2 wk, then itraconazole.
- #3Voriconazole— CNS blastomycosis (better CNS penetration than itraconazole).
- #4Fluconazole— Alternative if itraconazole not tolerated; less active in vitro.
Empiric therapy when resistant
CNS or refractory disease: liposomal amphotericin × 4–6 wk → voriconazole consolidation × ≥12 mo. ID consult.
Resistance notes
Resistance uncommon. Treatment duration ≥6–12 months. Itraconazole TDM (target trough ≥1 mg/L).
Pearls
Spectrum: pulmonary (most common, ranges from asymptomatic to ARDS), cutaneous (verrucous / ulcerative skin lesions — the classic clue), bone, GU, CNS. Less likely to be opportunistic than histo / cocci — affects immunocompetent hosts. Pulmonary blasto can mimic bacterial CAP, TB, or lung cancer. Outdoor / occupational exposure (hunters, foresters) common.