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