Blastomycosis: Clinical Presentation and Management
Clinical Presentation
Blastomycosis presents with a highly variable clinical spectrum, ranging from asymptomatic infection (occurring in at least 50% of exposed individuals) to life-threatening acute respiratory distress syndrome (ARDS). 1
Pulmonary Disease
The lungs are the primary site of infection following inhalation of conidia, with an incubation period of 30-45 days 1. Pulmonary presentations include:
- Acute pneumonia: Mimics community-acquired bacterial pneumonia with fever, productive cough, and lobar infiltrates 1
- Chronic pneumonia: Indistinguishable from tuberculosis or lung cancer, presenting with fibronodular infiltrates or mass lesions that can mimic bronchogenic carcinoma 1
- ARDS: Diffuse pulmonary infiltrates with fulminant progression and very high mortality 1
Disseminated Disease
Extrapulmonary dissemination occurs in 25-40% of patients 1. The most common sites are:
- Skin: Most frequent extrapulmonary site, often presenting without clinically active pulmonary disease 1
- Bones and joints: Osteoarticular involvement requiring prolonged therapy 1
- Genitourinary system: Particularly prostate involvement 1
- CNS: Rare in immunocompetent hosts but occurs in up to 40% of AIDS patients, manifesting as mass lesions or meningitis 1
Diagnostic Features
On microscopy, Blastomyces appears as round-to-oval multinucleate yeast cells (8-15 μm) with characteristic single broad-based budding 2. Urine antigen testing (sensitivity 85-93%, specificity 79-99%) is more sensitive than serum or bronchoalveolar lavage, though cross-reactivity with other endemic mycoses occurs 2.
Management Algorithm
Step 1: Assess Disease Severity and Site
All forms of blastomycosis require antifungal therapy to prevent extrapulmonary dissemination, even in mild cases. 1
Step 2: Initial Treatment Selection
For Moderately Severe to Severe Pulmonary or Disseminated Disease:
Start with liposomal amphotericin B 5 mg/kg/day (or lipid formulation amphotericin B 3-5 mg/kg/day, or amphotericin B deoxycholate 0.7-1 mg/kg/day) for 1-2 weeks until clinical improvement. 2, 1
- Lipid formulations are preferred due to reduced toxicity compared to deoxycholate 1
- Continue until patient shows clear clinical improvement (defervescence, improved oxygenation, hemodynamic stability)
For Mild to Moderate Pulmonary or Disseminated Disease:
Oral itraconazole 200 mg three times daily for 3 days (loading dose), then 200 mg once or twice daily for 6-12 months. 1
- Success rates of 90-95% in prospective studies 2, 1
- Capsule formulation requires food and gastric acidity; solution form taken on empty stomach 1
For CNS Blastomycosis:
Liposomal amphotericin B 5 mg/kg/day for 4-6 weeks, followed by step-down azole therapy for at least 12 months until CSF abnormalities resolve. 1
Azole options for CNS step-down therapy:
- Fluconazole 800 mg/day (excellent CSF penetration but less intrinsic activity) 1
- Itraconazole 200 mg 2-3 times daily (minimal CSF levels but greater activity against Blastomyces) 1
- Voriconazole 200-400 mg twice daily (good CSF penetration and excellent activity) 2, 1
Step 3: Step-Down Therapy
After clinical improvement with amphotericin B:
Transition to oral itraconazole 200 mg three times daily for 3 days, then 200 mg twice daily. 2, 1
Step 4: Duration of Therapy
- Pulmonary disease: 6-12 months total 1
- Osteoarticular disease: Minimum 12 months 1
- CNS disease: At least 12 months and until CSF abnormalities resolve 1
- Immunosuppressed patients: At least 12 months; lifelong suppressive therapy (itraconazole 200 mg/day) may be required if immunosuppression cannot be reversed 1
Step 5: Monitoring
Check serum itraconazole levels after at least 2 weeks of therapy to ensure adequate drug exposure. 1
Special Populations
Immunosuppressed Patients (Including AIDS)
Start with lipid formulation amphotericin B 3-5 mg/kg/day for 1-2 weeks, followed by itraconazole 200 mg three times daily for 3 days, then twice daily for at least 12 months. 1
- Obtain brain imaging to assess for CNS involvement even without neurological symptoms 1
- Consider lifelong suppressive therapy if immunosuppression persists 1
Pregnant Women
Lipid formulation amphotericin B 3-5 mg/kg/day is the only safe option; azoles are contraindicated during pregnancy. 1
Children
- Severe disease: Amphotericin B deoxycholate 0.7-1 mg/kg/day or lipid formulation 3-5 mg/kg/day for 1-2 weeks, followed by itraconazole 10 mg/kg/day (maximum 400 mg/day) for 12 months 1
- Mild to moderate disease: Itraconazole 10 mg/kg/day (maximum 400 mg/day) for 6-12 months 1
- Children tolerate deoxycholate amphotericin B better than adults 1
Alternative Agents
When itraconazole is not tolerated or contraindicated:
- Fluconazole 400-800 mg/day: Moderately successful (87% efficacy) but less effective than itraconazole 2, 1
- Voriconazole: Case series show outcomes similar to itraconazole, including favorable efficacy in CNS disease 2, 1
- Posaconazole and isavuconazole: Limited case report data suggest efficacy but insufficient experience 2, 1
Critical Pitfalls to Avoid
Do not withhold treatment in mild cases: Even asymptomatic or mild infections warrant treatment to prevent disseminated disease 1
Do not use azoles as primary therapy for CNS disease: Always start with amphotericin B for CNS involvement 1
Do not forget to check itraconazole levels: Therapeutic drug monitoring is essential to ensure adequate exposure 1
Do not use ketoconazole: Despite historical use, it is less effective and more toxic than itraconazole 1
Do not abbreviate therapy for osteoarticular disease: These cases require a full 12 months minimum 1
Corticosteroids for ARDS lack evidence: While used in some centers for blastomycosis-associated ARDS, there is little evidence for efficacy and no expert consensus 2
Diagnostic delays are common: Blastomycosis mimics bacterial pneumonia, tuberculosis, and malignancy; maintain high clinical suspicion in endemic areas 1