Colon nontumor
Infectious colitis (specific microorganisms)
Histoplasmosis

Author: Elliot Weisenberg, M.D.(see Authors page)

Revised: 27 July 2017, last major update July 2017

Copyright: (c) 2003-2017, PathologyOutlines.com, Inc.

PubMed Search: Histoplasmosis of colon
Cite this page: Histoplasmosis. PathologyOutlines.com website. http://pathologyoutlines.com/topic/colonhistoplasmosis.html. Accessed September 19th, 2017.
Definition / general
  • Colonic infection by Histoplasma capsulatum as part of disseminated histoplasmosis
Essential features
  • Histoplasma is a saprophyte that exists in the mycelial form in nature
  • Most Histoplasma is endemic to the Mississippi, Missouri and Ohio River valleys but disease occurs outside of these areas
  • Lungs are the initial site of infection which occurs after inhalation of spores where Histoplasma converts to a yeast form at body temperature
  • Overwhelming majority of cases are H. capsulatum var capsulatum; however in Africa disease may occur with H. capsulatum var. duboisii
  • Majority of infections are asymptomatic in immunocompetent hosts but clinical disease is common in immunosuppressed patients
  • Pulmonary disease is most common; however, as part of disseminated disease gastrointestinal histoplasmosis may cause diarrhea, bleeding, pain, nausea, vomiting, flu-like symptoms or obstruction
  • Large bowel is affected in approximately half of patients with gastrointestinal histoplasmosis and infection of multiple sites is common
  • Ulcers, nodules, hemorrhages, masses or lymphoid hyperplasia may be present and histopathologic findings include lymphohistiocytic infiltrates, the presence of variable numbers of primarily intracellular small yeast within histiocytes, lymphoid hyperplasia, infiltrates of eosinophils, neutrophils, necrotizing granulomas or plasma cells; importantly well formed granulomas are uncommon in disseminated disease
  • Pulmonary symptomatology may or may not be present in the face of disseminated disease
  • Itraconazole may be used as prophylaxis for immunosuppressed patients; disseminated disease is treated with amphotericin
Terminology
  • Cave disease, Darling disease, Ohio valley disease, reticuloendotheliosis, spelunkers lung; African histoplasmosis (var duboisii)
ICD-10 coding
  • B39-3
Epidemiology
  • Caused by inhaling the microconidia (spores) formed by the environmental mold
  • Most common in endemic areas of Mississippi, Ohio and Missouri River valleys but cases occur worldwide
  • Infection is very common in endemic areas but disease occurs in under 5% of immunocompetent individuals and up to 55% of immunocompromised patients
  • Uncommonly disease in Africa caused by var duboisii
  • Classically associated with soil contaminated by bird feces or bat guano; spelunking
Sites
  • Pulmonary infection is most common, sclerosing / fibrosing mediastinitis, pericarditis
  • Disseminated form affects multiple organs including the GI tract; most often the liver and spleen
  • In the GI tract the terminal ileum is most commonly involved
  • Involvement of the colon occurs in just over half of cases with GI tract involvement
  • Involvement of multiple sites in the GI tract is common
Pathophysiology
  • Yeast forms are phagocytized by neutrophils and pulmonary macrophages
  • Likely initially spread intracellularly to draining lymph nodes
  • In healthy individuals Histoplasma are contained by cellular immunity and disease generally does not occur
  • Disease is most common in the lungs
  • If not controlled by cellular immunity, dissemination may occur generally preferentially to reticuloendothelial sites with large numbers of mononuclear phagocytes especially the liver and spleen
  • Disease may be primary (acute infection or reinfection) or from activation of old infection with waning cellular immunity
  • Healthy individuals are usually asymptomatic; rarely infants may develop acute progressive disseminated histoplasmosis
  • Immunocompromised patients may develop acute or chronic progressive disseminated infection
Clinical features
  • Diarrhea, bleeding, pain, nausea, vomiting, flu-like symptoms or obstruction
  • Early diagnosis and treatment may avoid bowel perforation and hemorrhage
  • Pulmonary symptomatology may or may not be present
Diagnosis
  • Microscopy, examination of buffy coat for yeast in neutrophils and monocytes, Histoplasma capsulatum antigen in urine or serum (especially useful in disseminated disease) or serology (lacks sensitivity in AIDS patients), culture (slow, may take 4 to 6 weeks)
Radiology description
  • Bowel wall thickening or mass-like lesions
Case reports
Treatment
  • Itraconazole for prophylaxis of immunocompromised patients
  • Amphotericin for disseminated disease
Clinical images

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Large, polypoid, ulcerated, malignant-appearing tumor

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Ulcer in the sigmoid colon

Gross description
  • May cause gastrointestinal mucosal ulceration, may form polypoid lesions, strictures or a mass, grossly may simulate carcinoma, colon may appear normal, may have petechiae or hemorrhage
Microscopic (histologic) description
  • Yeast forms (2 - 5 um) with basophilic crescent shaped nucleus seen within macrophages, often with a pericellular halo
  • Organism are most easily found within necrotizing granulomas
  • Histopathologic findings include lymphohistiocytic infiltrates, the presence of variable numbers of primarily intracellular small yeast within histiocytes, lymphoid hyperplasia, infiltrates of eosinophils, neutrophils, necrotizing granulomas or plasma cells; importantly well formed granulomas are uncommon in disseminated disease
  • H. capsulatum var duboisii yeasts have a thicker wall and are much larger with a diameter up to 15 um
Microscopic (histologic) images

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Peripheral blood, Contributed
by Elliot Weisenberg, M.D.


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Numerous yeast forms

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Small rounded intracytoplasmic organisms

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Fig 2/3-H&E, 4-GMS

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Liver

Cytology description
  • Vacuolated single cells that may be suspicious for signet ring cell carcinoma; oval histiocytes with intracellular yeasts (Acta Cytol 1996;40:989)
Positive stains
Differential diagnosis
  • Cryptococcus: rare in colon; variably sized organisms (3 - 10 um)
  • Leishmania: rare in colon; GMS, Histoplasma lacks kinetoplasts
Board review question #1
    Which statement regarding histoplasmosis is true?

  1. Disease only occurs in immunosuppressed patients
  2. Gastrointestinal histoplasmosis is most common in the stomach
  3. Patients with intestinal histoplasmosis typically have no other disease involvement
  4. Restricted to the Mississippi, Missouri and Ohio River valleys
  5. Well formed granulomas are present only in a minority of cases of colonic histoplasmosis
Board review answer #1
E. Well formed granulomas are uncommon in disseminated histoplasmosis. Histoplasmosis is endemic in the Mississippi, Missouri and Ohio River valleys but disease occurs worldwide. Disease is much more common in immunocompromised patients and may occur in immunocompetent individuals. Gastrointestinal histoplasmosis is most common in the terminal ileum due to the density of lymphoid tissue in Peyer patches. Involvement of multiple sites in the GI tract is common.