Epidemiology & Risk Factors

Endemic areas: Great Lakes, Ohio & Mississippi River Valleys, Southeastern US.
Environment: Moist soil, decaying wood/leaves, organic debris near waterways.
Risk activities: Outdoor activities (hunting, camping, forestry).
Microbiology: Thermal dimorphic fungus (Blastomyces dermatitidis).
- Mold in environment at cool temperatures (25°C).
- Yeast in tissues at body temperature (37°C).

Clinical Features

Pulmonary (Most common):
- Acute: Fever, productive cough, pleuritic chest pain (mimics bacterial CAP).
- Chronic: Chronic cough, hemoptysis, night sweats, weight loss (mimics TB or lung carcinoma).
Extrapulmonary Dissemination (occurs in up to 50% of cases):
- Skin (Most common extrapulmonary site): Verrucous lesions with irregular/heaped-up borders or ulcerative lesions with microabscesses (mimics SCC or keratoacanthoma).
- Musculoskeletal: Osteomyelitis (vertebrae, long bones), lytic bone lesions, septic arthritis. c
- GU: Prostatitis, epididymo-orchitis.
- CNS: Meningitis, brain/epidural abscess (most common in immunocompromised).

Initial/Screening:
- Microscopy (Sputum, KOH mount, or tissue prep): Broad-based budding yeast (same size as RBC, ~8–15 µm, thick double-refractile cell wall).
- Urine/Serum Antigen Test: Rapid, high sensitivity; notable cross-reactivity with Histoplasma.
Confirmatory/Gold Standard: Fungal culture (takes 2–4 weeks) or tissue biopsy demonstrating characteristic yeast.
Imaging:
- CXR/CT: Consolidations, mass-like lesions, nodular infiltrates, or cavitary lesions.
Biopsy: Granulomatous inflammation with broad-based budding yeast.

Histoplasmosis: Diff by smaller, narrow-based budding yeast (2–5 µm, intracellular in macrophages), palatal/oral ulcers, hepatosplenomegaly, and hilar/mediastinal lymphadenopathy.
Coccidioidomycosis: Diff by endemic region (Southwestern US/AZ/CA), spherules containing endospores, erythema nodosum, and peripheral eosinophilia.
Squamous Cell Carcinoma (SCC): Diff by absence of fungal elements on skin biopsy; cutaneous blastomycosis lesions frequently mimic skin malignancy.
Tuberculosis: Diff by acid-fast bacilli (AFB) on stain, caseating granulomas, apical lung predilection, lack of broad-based yeast.

Mild-to-Moderate Disease (Pulmonary or Non-CNS Disseminated):
- First-line: Oral Itraconazole (6–12 months).
Severe Disease OR CNS Involvement OR Immunocompromised:
- First-line: Liposomal Amphotericin B (IV) for 1–2 weeks (or until clinical stabilization), followed by step-down oral Itraconazole for ≥12 months.
Refractory/Intolerant: Alternative azoles (e.g., Voriconazole, Posaconazole).

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