A 54-year-old man with HIV comes to the emergency department due to nonproductive cough, low-grade fevers, and worsening fatigue for the past month. He has also lost 3.6 kg (8 lb) over the same period. The patient does not take antiretroviral therapy consistently and has not followed up with his primary care physician for the past several months. Physical examination reveals hepatosplenomegaly. Laboratory testing shows pancytopenia and elevated liver aminotransferases. Bone marrow aspiration is performed, and light microscopy of the specimen is shown below. Which of the following is the most likely cause of this patient's current condition?

Question

A 54-year-old man with HIV comes to the emergency department due to nonproductive cough, low-grade fevers, and worsening fatigue for the past month.  He has also lost 3.6 kg (8 lb) over the same period.  The patient does not take antiretroviral therapy consistently and has not followed up with his primary care physician for the past several months.  Physical examination reveals hepatosplenomegaly.  Laboratory testing shows pancytopenia and elevated liver aminotransferases.  Bone marrow aspiration is performed, and light microscopy of the specimen is shown below.  Which of the following is the most likely cause of this patient's current condition?

Quizplus · Accepted Answer

11ec160b_389f_071f_9249_5d4d53e3ab75_MD0001_00 Light microscopy reveals several small, ovoid bodies within a macrophage, raising strong suspicion for Histoplasma capsulatum. This dimorphic fungus is transmitted by inhalation, converts to a yeast form in the lungs, and replicates within the phagosome of macrophages. Patients with intact immunity usually have an asymptomatic or self-limited pulmonary infection that is contained over time by the cell-mediated immune response. However, those with impaired immunity (eg, advanced AIDS) are at risk for dissemination through the reticuloendothelial system due to the organism's affinity for mononuclear phagocytic cells. Common manifestations include hepatosplenomegaly, lymphadenopathy, and pancytopenia. Ulcerated lesions on the tongue are also very characteristic of disseminated histoplasmosis. Disseminated infection is often diagnosed when histopathology shows oval or round yeasts within macrophages. Culture on Sabouraud agar grows hyphae (Histoplasma is a mold at cooler temperatures). Histoplasma antigen in blood and urine can also be detected by immunoassay. (Choice A) Aspergillus fumigatus is a monomorphic fungus with only a mold form. It is seen in tissue as septate hyphae with acute-angle V-shaped branching. (Choices B and D) Both Blastomyces and Coccidioides are dimorphic fungi that are inhaled into the lungs and replicate within macrophages. However, Blastomyces is a large yeast with thick walls and broad-based buds that disseminates primarily to the skin (not the reticuloendothelial system), and Coccidioides immitis appears as large, thick-walled spherules containing endospores. (Choice C) Candida albicans is an ovoid yeast that forms pseudohyphae. Mucocutaneous Candida infections (eg, thrush) are common in patients with HIV, but invasive infections (eg, pneumonia) are rare. In addition, Candida is an extracellular pathogen. (Choice E) Cryptococcus neoformans is a large yeast with a thick polysaccharide capsule. It can replicate within macrophages and cause pulmonary infection in patients with advanced AIDS. However, dissemination usually leads to meningoencephalitis (eg, slowly worsening headache, confusion, neurologic symptoms), not hepatosplenomegaly and pancytopenia. Educational objective: Histoplasma capsulatum is a dimorphic fungus that exists as a small, ovoid yeast at tissue temperatures. It replicates within macrophages and spreads through the lymphatic and reticuloendothelial system. Immunocompetent patients usually have an asymptomatic pulmonary infection, but those who are immunocompromised (eg, advanced AIDS) can develop disseminated disease to the liver, spleen, and bone marrow.

A 54-Year-Old Man with HIV Comes to the Emergency Department