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Skin-nontumor / Clinical Dermatology

Infectious disorders

Fungi - North American blastomycosis

Reviewer: Nat Pernick, M.D., Pathology Outlines.com, Inc. (see Reviewers page)
Revised: 25 July 2011, last major update July 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.


● Skin lesions usually secondary to pulmonary blastomycosis when soil containing mycelia is disturbed and airborne conidia are inhaled (Clin Microbiol Rev 2010;23:367); pulmonary disease may be subclinical
● Rarely occurs at site of penetrating injuries
● Due to Blastomyces dermatitidis, a spherical, double-contoured, 12 micron yeast that reproduces by budding
● Endemic areas are Mississippi, Missouri and Ohio river valleys (USA) and southern Canada
● Risk factors are immunosuppression, collagen vascular disease, being an outdoor worker, having a coworker with blastomycosis (Can J Infect Dis Med Microbiol 2009;20:117)
● May affect healthy patients via spore inhalation; usually men > women because they participate more in activities that disturb infected soil


● Histology, smears and culture using Sabouraud dextrose agar (Am J Surg Pathol 2010;34:256)

Case reports

● 53 year old African-American man with diabetes and knee mass (Arch Pathol Lab Med 2005;129:e132)


● Itraconazole or long term amphotericin

Clinical description

● Slowly enlarging verrucous plaques containing multiple small abscesses

Clinical images

Various images

Micro description

● Marked pseudoepitheliomatous hyperplasia of epidermis
● Granulomatous and neutrophilic infiltrate
● Fungi are within giant cells
Blastomyces dermatitidis is a 12 micron, spherical, double-contoured yeast with broad based buds

Micro images

Pseudoepitheliomatous hyperplasia, epidermal abscesses and prominent dermal infiltrate
High power shows fungal organisms

Budding yeast

Figure 1A: gross; 1B: atypical squamous proliferation infiltrating into deep dermis; 1C: intraepithelial neutrophilic abscesses; giant cell with round, broad based budding yeast

Giant cell with round, broad based budding yeast

Differential diagnosis

Well differentiated squamous cell carcinoma: may resemble pseudoepitheliomatous hyperplasia of fungal infection, but has marked atypia and invasion
Alternaria species: may have similar histologic features, but differentiate based on culture (J Cutan Pathol 2011 Jul 14 [Epub ahead of print])

Additional references

The University of Adelaide

End of Skin-nontumor / Clinical Dermatology > Infectious disorders > Fungi - North American blastomycosis

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