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Histoplasma capsulatum

Reviewers: Elliot Weisenberg, M.D. (see Reviewers page)
Revised: 6 September 2011, last major update September 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.

Clinical features

● Deep fungal infection indigenous to Ohio and Missouri River valleys and the Caribbean basin (eMedicine)
● See also Skin-nontumor topic
● Fungi are thermally dimorphic; spore producing hyphae outside body, but yeast at body temperature
● Infection due to inhaling dust or soil particles contaminated with bird or bat droppings
● "Capsulatum" is incorrect - no capsule is present
● In immunocompetent, generally causes a self-limited or latent infection, but chronic pneumonia preferentially involving lung apices associated with systemic symptoms and cough can occur; localized lung lesions, with or without lymph node involvement, are common; also localized lesions, often calcified, in adrenal, lymph nodes, liver, spleen, meninges; resembles tuberculosis with epitheliod granulomas with caseous necrosis; necrotic foci may coalesce to produce large areas of necrosis; with drug therapy or endogenous control, fibrosis and calcification occur, causing “tree bark” lesion
● In immunocompromised, disease is often virulent and widely disseminated
● If necessary, microbiologic studies, serology, or molecular studies are confirmatory


● Infection is incompletely understood, but is usually controlled by helper T-cells and heat shock protein that activate macrophages to kill yeast

Gross description

● Resembles tuberculosis, may see “tree-bark” appearance (due to fibrosis and calcification) or coin lesion

Gross images

Cut surface of fibrocaseous nodule

Micro description

● Diagnosis based on identifying small, budding, intracellular yeast in tissue, 2-5 microns
● Yeasts usually visible with H&E, but may need special stains; GMS more sensitive than PAS, but microcalcifications may create false positives
● No/minimal granulomas in immunosuppressed or neonates; yeasts fill histiocytes and are widely disseminated

Micro images

Contributed by Dr. Jamie Shutter, Florida: left images-H&E; right images-GMS

GMS staining

Negative stains

● Acid-fast

End of Lung-nontumor > Infections > Histoplasma capsulatum

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