8 October 2009 – Case of the Week #159
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Case of the Week #159
An otherwise healthy 31-year-old woman presented to a hospital in Montreal, Canada with an “enlarged stomach lesion” by endoscopy. A gastric biopsy was performed.
What is your diagnosis?
Histoplasmosis of the stomach
Histoplasma capsulatum is a fungus commonly found throughout the world. In the U.S., it is endemic in the Ohio and Mississippi River valleys (eMedicine), particularly in caves and bat and bird droppings. It is frequently found in the lungs, but can affect any site. In the G.I. tract, it may cause nausea, vomiting, diarrhea, hepatosplenomegaly and possibly perforation and peritonitis. Histoplasma often infects patients with AIDS or other immunosuppressive disorders (Dis Col Rect 1991;34:185) and is often severe or fatal (Microbes Infect 2008;10:973).
Patients may present with mucosal ulceration, hemorrhage or submucosal plaques or nodules, but 25% of patients have no endoscopic findings. Microscopically, there are intracellular spores up to 4 microns with rigid walls and retracted cytoplasm. The organisms have a clear zone around a central blue nucleus, which gives the cell membrane the appearance of a capsule - hence the name of the organism.
Diagnosis is based on histology and culture, as well as rapid antigen / antibody tests of blood, urine or tissue (Curr Opin Infect Dis 2008;21:421). Skin tests confirm exposure, but not infection. A bone marrow biopsy may be helpful in early diagnosis, which is particularly important in disseminated disease (Arch Pathol Lab Med 2006;130:120).
Histoplasmosis of the stomach may clinically resemble a gastric ulcer (Rev Gastroenterol Peru 2003;23:221). The microscopic differential diagnosis includes Candida glabrata, the second most common Candida species in U.S. hospitalized patients. In tissue, it present as yeasts, 3-5 microns in size, which are difficult to visualize on H&E stained slides but can be detected with GMS. Typically no hyphal elements are found (Dermatol Online J 2008;14:15). It can differentiated from Histoplasma based on H&E appearance (histoplasma spores are identifiable) and culture. Other disorders that may appear similar include Leishmania infection, Mycobacterium avium-intracellulare, Whipple’s disease, Cryptococcosis and malakoplakia.
Treatment for Histoplasmosis is generally a course of antibiotics from 3 to 18 months. Relapses are common.
Nat Pernick, M.D., President,
and Kara Hamilton, M.S., Assistant Medical Editor
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