September 2006

Fig.5

Diagnosis: Disseminated blastomycosis.

Histopathology: Skin biopsies were performed. Two biopsies were sent for H&E. One biopsy was sent for culture. H&E revealed pseudoepitheliomatous hyperplasia, a neutrophilic infiltrate, and large yeast forms consistent with blastomycosis(Fig,4). A GMS stain (Fig.5) highlighted scattered fungal forms and a "broad-based bud."

Discussion: North American blastomycosis, also called Chicago disease or Gilchrist disease, is caused by Blastomycosis dermatitidis. B. dermatitidis is a thermally dimorphic saprophyte which is endemic to North America, especially in lake and river valleys and the Southeast.
When spores are inhaled, they transform into broad-based budding yeast which initially infect the lungs. Subsequent hematogenous spread allows secondary infection of the skin, pleura, bone, genitourinary system, and central nervous system.
The clinical severity of blastomycosis varies greatly. In up to half of patients, pulmonary infection is subclinical. Nonspecific symptoms such as fever, fatigue, and malaise are frequent. Diagnosis is often delayed. Adult men more often develop systemic infection, while children more often develop acute pulmonary disease. Blastomycosis occurs at an increased rate and with increased mortality in African-Americans.
The skin is the most frequent extrapulmonary site for blastomycosis. Spread of infection to the skin typically occurs during the symptomatic, primary infection. Cutaneous infection rarely occurs as a result of direct inoculation. Cutaneous lesions tend to be verrucous, papulopustular, scarring, and/or ulcerative, and on exposed skin. Cutaneous lesions may mimic a number of conditions including keratoacanthoma, squamous cell carcinoma, basal cell carcinoma, pyoderma gangrenosum, verruca vulgaris, sarcoidosis, tuberculosis, nocardiosis, and other systemic fungal infections.
Treatment is typically systemic amphotericin B. Itraconazole or ketoconazole may also be used.

References:

1. Bradsher RW, Chapman SW, Pappas PG. Blastomycosis. Infect Dis Clin North Am. Mar 2003;17(1):21-40, vii.
2. Auger I, Gagne E, Alain J, Pelletier R. Cutaneous blastomycosis: A clue for reassessing the recent diagnosis of pulmonary sarcoidosis. Arch Dermatol. Jun 2006;142(6):795-797.
3. James AJ, Bender MM, Chen AJ, Bayer-Garner IB, Hsu S. Tender nodules on the extremities. Dermatol Online J. Dec 2003;9(5):20.
4. Cano MV, Ponce-de-Leon GF, Tippen S, Lindsley MD, Warwick M, Hajjeh RA. Blastomycosis in Missouri: epidemiology and risk factors for endemic disease. Epidemiol Infect. Oct 2003;131(2):907-914.

This case is presented by Drs. David Berk and Amy Cheng with special thanks to Drs. Grace Bandow, Anne Lind, Beatriz Tapia, and Lynn Cornelius.