Histoplasmosis
Cornelia S. L. Mller, MD
Bruce R. Smoller, MD
Key Facts
Terminology
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Systemic fungal infection caused by yeast Histoplasma capsulatum var. capsulatum
Clinical Issues
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Widely distributed with endemic occurrence in eastern and central United States
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Skin is usually involved secondarily following primary infection of lung
Microscopic Pathology
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Usually caseating or noncaseating granulomatous dermal infiltrate
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Intracellular 2-4 µm yeasts surrounded by clear space (pseudocapsule) within macrophages can be highlighted with GMS or PAS stains
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Top Differential Diagnoses
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Leishmaniasis
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Penicilliosis
Histoplasmosis of the tongue presented as a punched-out ulcer in this patient. (Courtesy L. Thompson, MD.) |
A biopsy of histoplasmosis of the skin demonstrates numerous yeast  surrounded by a clear halo (pseudocapsule) within macrophages. (Courtesy S. Billings, MD.) |
TERMINOLOGY
Synonyms
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Darling disease, histo
Definitions
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Systemic fungal infection caused by yeast Histoplasma capsulatum var. capsulatum
ETIOLOGY/PATHOGENESIS
Environmental Exposure
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Exposure to soil contaminated with bird and bat droppings
CLINICAL ISSUES
Epidemiology
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Incidence
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Widely distributed with endemic occurrence in eastern and central United States
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