By Gary M. White, MD
A solitary verrucous plaque on the arm.
Blastomycosis is a fungal infection by Blastomyces dermatitidis. It is endemic to the Ohio and Mississippi river basins. It is round yeast (diameter 8-15 um) with broad-based budding and doubly refractile walls. Most cases of blastomycosis begin as a primary pulmonary infection after inhalation of the organism.
Clinically, it usually presents as a verrucous plaque or multiple verrucous papules. Other presentations include subcutaneous nodules and ulcers with raised borders.
Diagnosis is usually made by skin biopsy from which the organisms may be identified and cultured. The laboratory should be notified of the suspected diagnosis prior to culture. Alternatively, histology (e.g., large fungal organisms with broad-based budding), urine antigen and complement fixation antibody testing may be done.
An infectious disease expert should be consulted. In the past, Amphotericin B and itraconazole have been successful. For non-life-threatening disease, itraconazole 400 mg/day for at least 6 months or alternatively fluconazole (400-800 mg/day for 6 months) have been used. For life-threatening, treatment-resistant or aggressive disease, many have recommended amphotericin B.
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