USMLE-Rx Step 2 Practice Q's

USMLE-Rx Step 2 Qmax Challenge #21225

Check out today’s Step 2 CK Qmax Question Challenge.

Know the answer? Post it in the comments below! Don’t forget to check back for an update with the correct answer and explanation (we’ll post it in the comments section below).

USMLE-Rx Step 2 Qmax Challenge #21225An 8-year-old boy is brought to the physician because of refusal to walk for 3 days. On questioning, he states that both his legs hurt. His mother states he has “not been himself” for the past month and has been sleeping much more than usual. His temperature is 38.4°C (101.1°F), heart rate is 164/min, respiratory rate is 42/min, and blood pressure is 90/54 mm Hg. The child is pale and listless. Severe hepatomegaly is noted. The child also limps when walking. There are no obvious deformities of the lower extremities or hip, knee, or ankle joints. A peripheral blood smear is shown below. Laboratory tests show:

WBC count: 9,500/mm³
Hemoglobin: 8.9 g/dL
Platelet count: 75,000/mm³
Na+: 135 mEq/L
K+: 4.0 mEq/L
Cl-: 104 mEq/L
Blood urea nitrogen: 8 mg/dL
Creatinine: 0.6 mg/dL

What is the best step in the management of this patient?

A. A CT scan
B. Bone marrow biopsy
C. Emergent chemotherapy
D. Multiple-gated acquisition scans
E. Platelet transfusion

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5 replies »

  1. The correct answer is B. This patient is presenting with a classic case of acute lymphoblastic leukemia (ALL). Most children with ALL have anemia and/or thrombocytopenia with either normal or slightly increased WBC counts and lymphoblasts on peripheral smear. Although ALL may be difficult to differentiate from acute myeloid leukemia, the next step in treatment is the same for both illnesses. Patient evaluation prior to beginning therapy requires a complete blood cell count, chemistry studies assessing major organ function, a bone marrow biopsy, and a lumbar puncture to rule out occult central nervous system involvement. The latter two procedures are generally performed together so that conscious sedation is necessary only once. Bone marrow samples should also be sent for flow cytometry and cytogenetics. The most common cytogenetic abnormalities in ALL in children are hyperdiploidy and t(12;21), both of which occur in about 25% of cases and confer a good prognosis. Other translocations, such as t(9;22) and t(4;11) are rare. A key note is that a ‘limping child’ must be evaluated for leukemia until otherwise proven.

    A is not correct. A CT scan can be useful to assess the degree of lymphadenopathy in patients with mediastinal masses. It can also be used to identify malignant invasion of other organs such as the liver, spleen, lymph nodes, brain, and kidneys. However, it is not the best next step in management.

    C is not correct. Chemotherapy is preserved for established cases of cancer. It should be initiated without delay once a definitive diagnosis is made.

    D is not correct. Multiple-gated acquisition (MUGA) scans along with electrocardiograms (ECGs) are used because many chemotherapeutic agents that are used are cardiotoxic. These are ordered once a definitive diagnosis is made and prior to initiating therapy.

    E is not correct. A patient with a platelet count of 75,000/mm³ is not considered at risk for spontaneous bleeding. An emergent platelet transfusion would be considered for a patient with a platelet count of 25,000/mm³ and would be indicated in one with a platelet count 10,000/mm³ or lower.

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