A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 32-year-old woman with a history of HIV infection and a CD4+ count of 90 cells/mm³ presents with a 3-week history of fever, night sweats, and weight loss. She denies cough or hemoptysis. On physical examination, she has palpable cervical lymphadenopathy, and her abdomen is soft with mild hepatomegaly. Laboratory studies reveal anemia and elevated serum levels of interleukin-6. A chest X-ray shows clear lung fields. Which of the following is the most likely organism responsible for her symptoms?
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A
Histoplasma capsulatumIncorrect. Histoplasmosis causes disseminated illness in AIDS but typically shows pulmonary infiltrates and oral ulcers, not isolated lymphadenopathy with hepatomegaly.
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B
Mycobacterium tuberculosisIncorrect. TB usually presents with cough and pulmonary involvement; clear lung fields and absent respiratory symptoms make active pulmonary TB unlikely here.
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C
Mycobacterium avium complexCorrect. Disseminated MAC in advanced AIDS (CD4 under 100) classically causes fevers, weight loss, lymphadenopathy, hepatomegaly, and elevated IL-6.
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D
Pneumocystis jiroveciiIncorrect. Pneumocystis jirovecii causes diffuse interstitial pneumonia with hypoxia; absence of cough and clear chest X-ray rule it out.
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E
Cryptococcus neoformansIncorrect. Cryptococcus typically causes meningitis or pulmonary disease in AIDS; no headache, mental status changes, or lung findings are described here.
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Answer: C. The patient presents with fever, night sweats, weight loss, lymphadenopathy, and hepatomegaly in the context of advanced HIV and immunosuppression. These are indicative of a disseminated Mycobacterium avium complex (MAC) infection, especially with the elevated interleukin-6 levels. M. tuberculosis (A) typically presents with pulmonary involvement, which is absent here. Histoplasma (B) and Cryptococcus (E) can cause similar symptoms but are less likely given the specific presentation and lab findings. Pneumocystis (D) primarily causes respiratory symptoms.