Topic Completed: 1 September 2011

Minor changes: 28 July 2020

Copyright: 2003-2021,, Inc.

PubMed search: Histoplasma capsulatum [title] pulmonary

Elliot Weisenberg, M.D.
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Cite this page: Weisenberg E. Histoplasma. website. Accessed October 15th, 2021.
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
Microscopic (histologic) 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
Microscopic (histologic) images

Contributed by Jamie Shutter, M.D.
Left images: H&E; right images: GMS Left images: H&E; right images: GMS Left images: H&E; right images: GMS Left images: H&E; right images: GMS

Left images: H&E; right images: GMS

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GMS staining

GMS staining

Negative stains
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