USMLE-Rx Step 3 Practice Q's

USMLE-Rx Step 3 Qmax Challenge #31030

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USMLE-Rx Step 3 Qmax Challenge #31030An 11-year-old boy comes to the emergency department because of fever, headache, rash, and mild abdominal pain. He states that he was hiking in the Appalachian Mountains of North Carolina for 4 days as part of a Boy Scout trip. His temperature is 38.3°C (101°F), pulse is 115/min, blood pressure is 95/60 mm Hg, respiratory rate is 14/min, and oxygen saturation is 98% on room air. Examination is most notable for the skin finding shown in the image. Laboratory tests show a WBC count of 16,000/mm³, hematocrit of 46%, and platelet count of 412,000/mm³.

The patient has which of the following conditions that is also reportable to the Centers for Disease Control and Prevention?

A. Ehrlichiosis
B. Lyme disease
C. Meningococcemia
D. Rocky Mountain spotted fever
E. Staphylococcal cellulitis


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11 replies »

  1. Its D Rocky mountain Spotted Fever (RMSF) given the typical maculopapular rash, fever, headache and travel to North Carolina. RMSF is caused by Ricketsia ricketsiae transmitted by Dermacantor (hard tick). The rash is due to vasculitis of small blood vessels as Ricketsiae have a special tropism for endothelial cells causing endarteritis

    I t can not be Ehrlichiosis as WBC and platelets are not decreased
    Cannot be Lyme as there is no target rash
    Cannot be meningococcemia as no purpura present
    Cannot be staphylococcal cellulitis as there is no indurated red hot lesion with a toxic patient


  2. The correct answer is D. This patient has developed Rocky Mountain spotted fever (RMSF), which is classically associated with fever, rash, and headache. The rash typically consists of blanching erythematous macules around the wrists and ankles. The lesions spread centripetally, becoming maculopapular with central petechiae in advanced stages of disease. The ticks that carry the causative organism are most often found in wooded areas. A high clinical suspicion is required because in the early stages of disease the symptoms are often nonspecific and it is in the earliest stages of disease that the therapies are most beneficial. RMSF is reportable to the Centers for Disease Control and Prevention (CDC).

    A is not correct. Although differentiating between the clinical diagnosis of RMSF and human ehrlichiosis is often difficult, ehrlichiosis tends to present with leukopenia, which is not seen in this patient. In addition, the tick vector differs in these two diseases. However, the treatment for both would be doxycycline with similar dosing strategies.

    B is not correct. Although the patient has been hiking in an area endemic for Lyme disease in a susceptible time of the year, the rash of Lyme disease is classically a “bull’s eye” rash of erythema with central clearing.

    C is not correct. The patient’s symptom triad of fever, rash, and headache and exposure to college dormitories increases the suspicion for meningococcemia. However, the rash is atypical for this disease, as the rash in meningococcemia typically begins on the trunk and legs, with a confluence of lesions resulting in hemorrhagic patches with central necrosis. Acquisition of the infection during the hiking trip is more consistent with an arthropod-borne illness.

    E is not correct. Staphylococcal cellulitis would not be compatible with the patient’s presentation and petechial rash. Furthermore, cellulitis is not a condition reportable to the CDC.


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