USMLE-Rx Step 1 Qmax Challenge #4019

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USMLE-Rx Step 1 Qmax Challenge #4019A 46-year-old man presents with a temperature of 38.6°C (101.5°F). He was fine 2 weeks ago, but started feeling poorly a few days ago after a dental examination. Physical examination reveals tender raised lesions on the beds of his fingers and toes, and painless, erythematous lesions on his palms and soles, like those in the images. On further questioning, the physician discovers that the man has a history of rheumatic fever as a child. Blood cultures are drawn.

The most likely causative organism will have which characteristics?

A. Gram-positive cocci, catalase-negative, β-hemolytic, bacitracin-resistant
B. Gram-positive cocci, catalase-negative, β-hemolytic, bacitracin-sensitive
C. Gram-positive cocci, catalase-negative, α-hemolytic, optochin-resistant
D. Gram-positive cocci, catalase-positive
E. Gram-positive, weakly acid-fast rod


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14 thoughts on “USMLE-Rx Step 1 Qmax Challenge #4019”

  1. c
    manifestations are due to emboli from infective endocarditis involving heart valves. Rheumatic heart disease caused the predisposing damaged heart valves

  2. Why doesn’t this question have an official answer? I’m between 2 answers B and C. C makes sense in the situation but does it usually present with a lesion? I only B presents with a lesion

  3. B..Group A beta hemolytic S.pyogenes Bacitracin sensitive. History of Rheumatic fever is associated with GAS. Abs to heart tissue 2 weeks post Strep pharyngitis. Joint inflammation, carditis, erythema Magnatum, etc

  4. FirstAid-RStigall

    The correct answer is C. The patient is likely suffering from subacute bacterial endocarditis, likely precipitated by his recent dental examination. He has classic symptoms of Osler’s nodes (tender raised lesions on finger or toe pads–left-hand image) and Janeway’s lesions (non-tender erythematous lesions on the palms or soles, right-hand image). Viridans streptococci are a common cause of this form of endocarditis, which generally occurs in the setting of dental procedures on patients with diseased heart valves. Viridans streptococci are gram-positive, catalase-negative, ?-hemolytic cocci.

    A is not correct. Streptococcus agalactiae, or Group B streptococci, are gram-positive, ?-hemolytic cocci. They are bacitracin resistant. They cause pneumonia, meningitis, and sepsis, mainly in babies, and thus are unlikely to be responsible for this patient’s condition.

    B is not correct. Streptococcus pyogenes is a gram-positive, ?-hemolytic group A streptococcus. These organisms are bacitracin sensitive. This organism is most commonly associated with illnesses such as pharyngitis, cellulitis, impetigo, scarlet fever, toxic shock syndrome, rheumatic fever, and acute glomerulonephritis—but not with endocarditis.

    D is not correct. Staphylococcus aureus is a common cause of acute endocarditis. These organisms often are the culprit in the setting of previously healthy intravenous drug users. They are gram-positive, catalase-positive cocci.

    E is not correct. Nocardia asteroides is a gram-positive, weakly acid-fast rod. It is known to cause pulmonary infection in immunocompromised individuals. It is not known to cause bacterial endocarditis.

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