Blastomycosis is a pulmonary disease caused by inhaling spores of the dimorphic fungus Blastomyces dermatitidis; occasionally, the fungi spread hematogenously, causing extrapulmonary disease. Symptoms result from pneumonia or from dissemination to multiple organs, most commonly the skin. Diagnosis is clinical, by chest x-ray, or both and is confirmed by laboratory identification of the fungi. Treatment is with itraconazole, fluconazole, or amphotericin B.

(See also the Infectious Diseases Society of America's Practice Guidelines for the Management of Patients with Blastomycosis.)

In North America, the endemic area for blastomycosis includes

• Ohio–Mississippi River valleys (extending into the middle Atlantic and Southeastern states)
• Northern Midwest
• Upstate New York
• Southern Canada

Infection also occurs in the Middle East and Africa.

Immunocompetent people can contract this infection. Although blastomycosis may be more common and more severe in immunocompromised patients, it is a less common opportunistic infection than histoplasmosis or coccidioidomycosis.

B. dermatitidis grows as a mold at room temperature in soil enriched with animal excreta and in moist, decaying, acidic organic material, often near rivers. In the lungs, inhaled spores convert into large (15 to 20 μm) invasive yeasts, which form characteristic broad-based buds.

Once in the lungs, infection may

• Remain localized in the lungs
• Disseminate hematogenously

Hematogenous dissemination can cause focal infection in numerous organs, including the skin, prostate, epididymides, testes, kidneys, vertebrae, ends of long bones, subcutaneous tissues, brain, oral or nasal mucosa, thyroid, lymph nodes, and bone marrow.

Symptoms and Signs

Pulmonary: Pulmonary blastomycosis may be asymptomatic or cause an acute, self-limited disease that often goes unrecognized. It can also begin insidiously and develop into a chronic, progressive infection. Symptoms include a productive or dry hacking cough, chest pain, dyspnea, fever, chills, and drenching sweats.

Pleural effusion occurs occasionally. Some patients have rapidly progressive infections, and acute respiratory distress syndrome may develop.

Extrapulmonary: In extrapulmonary disseminated blastomycosis, symptoms depend on the organ involved. Skin lesions are by far the most common; they may be single or multiple and may occur with or without clinically apparent pulmonary involvement. Papules or papulopustules usually appear on exposed surfaces and spread slowly. Painless miliary abscesses, varying from pinpoint to 1 mm in diameter, develop on the advancing borders. Irregular, wartlike papillae may form on surfaces. As lesions enlarge, the centers heal, forming atrophic scars. When fully developed, an individual lesion appears as an elevated verrucous patch, usually ≥ 2 cm wide with an abruptly sloping, purplish red, abscess-studded border. Ulceration may occur if bacterial superinfection is present.

If bone lesions develop, overlying areas are sometimes swollen, warm, and tender. Genital lesions cause painful epididymal swelling, deep perineal discomfort, or prostatic tenderness detected during rectal examination.

Blastomycosis—Extrapulmonary (Bullae)

Blastomycosis—Extrapulmonary (Verrucous Appearance)

Diagnosis

• Chest x-ray
• Fungal cultures

A chest x-ray should be taken. Focal or diffuse infiltrates may be present, sometimes as patchy bronchopneumonia fanning out from the hilum. These findings must be distinguished from other causes of pneumonia (eg, other mycoses, TB, tumors). Skin lesions can be mistaken for sporotrichosis, TB, iodism, or basal cell carcinoma. Genital involvement may mimic TB.

Blastomycosis—Pulmonary

Cultures of infected material are done; they are definitive when positive. The organism's characteristic appearance, seen during microscopic examination of tissues or sputum, is also frequently diagnostic. Serologic testing is not sensitive but is useful if positive.

Treatment

• For mild to moderate disease, itraconazoleSome Trade Names
  SPORANOX
  Click for Drug Monograph
  
• For severe, life-threatening infection, amphotericin BSome Trade Names
  ABELCET
  AMBISOME
  AMPHOCIN
  AMPHOTEC
  Click for Drug Monograph
  

Untreated blastomycosis is usually slowly progressive and is rarely ultimately fatal. Treatment depends on severity of the infection. For mild to moderate disease, itraconazoleSome Trade Names
SPORANOX
Click for Drug Monograph
200 to 400 mg po once/day is used. FluconazoleSome Trade Names
DIFLUCAN
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appears less effective, but 400 to 800 mg po once/day may be tried in itraconazoleSome Trade Names
SPORANOX
Click for Drug Monograph
-intolerant patients with mild disease. For severe, life-threatening infections, IV amphotericin BSome Trade Names
ABELCET
AMBISOME
AMPHOCIN
AMPHOTEC
Click for Drug Monograph
is usually effective.

VoriconazoleSome Trade Names
VFEND
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and posaconazoleSome Trade Names
NOXAFIL
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are highly active against B. dermatitidis, but their role has not yet been defined.

Last full review/revision April 2009 by Alan M. Sugar, MD

Content last modified February 2012