A 21-year-old previously healthy man comes to the office due to fever, malaise, myalgia, and nonproductive cough. His symptoms began 2 weeks after returning from exploring caves in Missouri. The patient does not use tobacco, alcohol, or illicit drugs. Temperature is 38.3 C (100.9 F), blood pressure is 120/70 mm Hg, pulse is 96/min, and respirations are 16/min. Physical examination reveals lung crackles. Chest x-ray shows patchy parenchymal infiltrates with enlarged mediastinal and hilar lymph nodes. Which of the following is most likely to be present in this patient's pulmonary lesions?

Question

A 21-year-old previously healthy man comes to the office due to fever, malaise, myalgia, and nonproductive cough.  His symptoms began 2 weeks after returning from exploring caves in Missouri.  The patient does not use tobacco, alcohol, or illicit drugs.  Temperature is 38.3 C (100.9 F), blood pressure is 120/70 mm Hg, pulse is 96/min, and respirations are 16/min.  Physical examination reveals lung crackles.  Chest x-ray shows patchy parenchymal infiltrates with enlarged mediastinal and hilar lymph nodes.  Which of the following is most likely to be present in this patient's pulmonary lesions?

Quizplus · Accepted Answer

11ec160b_389e_1cbd_9249_c349cf22b7ff_MD0001_00 Histoplasma capsulatum is a dimorphic fungus that is endemic to the Ohio and Mississippi River valleys. It exists as a filamentous mold in the environment and is found primarily in soil contaminated with bird or bat droppings. Therefore, infected patients often report a history of exploring caves (exposure to bats) or cleaning bird cages or coops. H capsulatum is transmitted when fungal spores from contaminated soil are inhaled into the alveoli. At body temperature, the spores germinate into yeasts and are subsequently phagocytosed by alveolar macrophages. The pathogen eludes macrophage-mediated destruction by preventing acidification of the phagolysosome and initially replicates in an unchecked fashion. Therefore, light microscopy of the affected areas reveals macrophages with intracellular ovoid or round yeasts. Spread to the draining mediastinal and hilar lymph nodes prompts a cell-mediated immune response that helps contain the infection within caseating granulomas (similar to the immune response to Mycobacterium tuberculosis). Patients with intact immune systems usually remain asymptomatic, but a minority develop subacute pneumonia (ie, cough, fever, pleuritic chest pain, pulmonary infiltrates) with hilar and mediastinal lymphadenopathy. In immunocompromised patients (eg, AIDS), infected macrophages can spread the organism throughout the reticuloendothelial system, resulting in widespread disseminated disease. (Choice A) Cryptococcus neoformans appears as a budding yeast with a thick polysaccharide capsule. Although C neoformans is often transmitted from soil contaminated with bird (pigeon) droppings, this pathogen primarily causes central nervous system disease (meningoencephalitis) in patients with severe immunocompromise (eg, advanced AIDS). (Choice C) Coccidioides immitis appears as spherules packed with endospores. Coccidioides can cause pulmonary disease in healthy individuals, but this pathogen is endemic to the southwestern United States deserts (not Missouri) and is not associated with cave exploration. (Choice D) Aspergillus fumigatus appears as septate hyphae with V-shaped branching. Invasive pulmonary aspergillosis is seen primarily in patients with severe immunocompromise (eg, AIDS). (Choice E) Candida species are yeasts that form pseudohyphae and blastoconidia (budded cells off of the pseudohyphae). Patients with intact immune systems rarely develop invasive Candida infections. Educational objective: Histoplasma capsulatum is endemic to the Ohio and Mississippi River valleys and is found primarily in soil contaminated with bird or bat droppings. It exists in tissues as an ovoid/round yeast predominantly within the intracellular space of macrophages. Immunocompetent patients are often asymptomatic but can infrequently develop subacute pneumonia with hilar and mediastinal lymphadenopathy.

A 21-Year-Old Previously Healthy Man Comes to the Office Due