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Discussion Starter · #1 ·
A 54-year-old Caucasian male diagnosed with HIV infection two years ago develops cough, low-grade fevers and hepatosplenomegaly. He has lost eight pounds over the past month. A light microscopy image of a bone marrow aspirate is shown below.

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Which of the following is the most likely cause of this patient's condition?

A. Rhizopus species
B. Aspergillus fumigatus
C. Candida albicans
D. Cryptococcus neoformans
E. Blastomyces dermatitidis
F. Histoplasma capsulaturn
G. Coccidioides immitis
H. Sporothrix schenckii
 

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Discussion Starter · #7 ·
F) Histoplasma capsulaturn

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This image shows small ovoid bodies within a macrophage. Histoplasma capsulatum is the only answer choice listed that can survive intracellularly and cause systemic disease. In non-immunocompromised individuals, Histoplasma infection is asymptomatic or may produce a self-limiting pulmonary disease. Immunocompromised individuals can develop systemic histoplasmosis that may prove fatal. Disseminated histoplasmosis causes hepatosplenomegaly because of its predilection for the reticuloendothelial system. Ulcerated lesions on the tongue are also very characteristic of disseminated histoplasmosis.

DX
Chest x-ray of a patient with disseminated histoplasmosis may show diffuse pulmonary infiltrates with hilar lymphadenopathy. In chronic lung disease, the radiographic changes resemble those of pulmonary tuberculosis: cavitary lesions form in the upper lung lobes, and calcified nodes and fibrotic scarring may also be present.

Examination of lung biopsy specimens and bone marrow aspirates reveals oval or round yeasts within macrophages. Culture on Sabouraud's agar will grow hyphae (as Histoplasma is a dimorphic fungus). Histoplasma antigen in blood and urine can be detected by radioimmunoassay. Serologic tests (e.g. complement fixation immunodiffusion) can be used to measure the level of anti-1-Iistoplasme antibodies
 
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