If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 3 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.
This month’s stumper
A 52-year-old woman presents to her physician with a rash that involves her face, back, arms and hands. She denies any recent insect or tick bites, or exposure to poison ivy. Her past medical history is notable for hypertension and diabetes, and she takes hydrochlorothiazide, lisinopril and glyburide. She has been taking these medications for the past three years. She denies smoking, consuming alcohol or using illicit substances. Review of systems reveals that she has experienced fatigue and weight loss for about five months. She has also noticed difficulty rising out of a chair.
On physical examination, her temperature is 37.2º C (99º F), blood pressure is 134/71 mm Hg, pulse is 89 beats per minute and oxygenation is 97 percent on room air. Her face has a fine rash surrounding her eyes, and the skin overlying her distal and proximal interphalangeal joints is thickened and erythematous. Her chest and cardiovascular exams are unremarkable. Her abdominal exam reveals no organomegaly, distention, or tenderness. Peripheral exam reveals no clubbing, cyanosis, or edema. Neurologically, she has a three-out-of-five strength with flexion of both her hips. She has intact sensation, normal reflexes throughout, and downgoing Babinski reflexes bilaterally.
Laboratory data are:
- White blood cells: 9,300/mm3.
- Hematocrit: 37 percent.
- Platelets: 247,000/mm3.
- Urea nitrogen: 17 mg/dL.
- Creatinine: 0.9 mg/dL.
- Anti-Jo antibody: Positive in 1:256 titer.
- Glucose: 131 mg/dL
- Potassium: 4.3 mEq/L.
- Phosphate: 3.1 mg/dL.
- Calcium: 8.6 mg/dL.
- Magnesium: 2.1 mg/dL
- Erythrocyte sedimentation rate: 85 mm/hr.
- Iron: 24 mg/dL.
- Iron-binding capacity: 401 g/dL.
- Ferritin: 709 ng/mL (normal: 30-300 ng/mL).
- Creatine kinase: 1,787 U/L.
- ANA: Positive in 1:128 titer.
The patient is started on high-dose steroids. Which of the following would be the next step in management?
A. CT of the head.
B. CT of the chest, abdomen and pelvis.
C. Intravenous immunoglobulin therapy.
D. Tensilon test.
E. No further intervention is required.
The correct answer is B.
Kaplan Medical explains why
Dermatomyositis (DM), the condition with which this patient presents, can be the heralding presentation of an underlying malignancy. One in four patients presenting with DM has an occult malignancy. This high statistical documentation warrants the search, on a routine basis, for malignancy in someone who is diagnosed with DM. A good start is with a CT scan of the chest, abdomen, and pelvis. The cancers that are most associated with DM, in descending order, are ovarian, lung, pancreatic, gastric, colorectal and non-Hodgkin lymphoma.
Why the other answers are wrong
Choice A: A CT of the head is not warranted because this patient's weakness seems to be at the level of the muscles or lower motor neuron, not the upper motor neuron. An intracranial malignancy is unlikely to present with DM.
Choice C: Intravenous immunoglobulin therapy would be used for Guillain-Barré syndrome. This disorder presents with distal to proximal weakness.
Choice D: The Tensilon test is used in the evaluation of myasthenia gravis.
Choice E: No further intervention is inappropriate because evaluation for an underlying malignancy for improving this patient's mortality.
Tips to remember
- This patient presents with dermatomyositis, with a classic heliotrope rash, Gottron papules on the fingers, and proximal muscle weakness.
- The anti-Jo antibody assay is positive, and the creatine kinase is elevated.
- Muscle biopsy will likely confirm the diagnosis.
- There is an association of dermatomyositis with cancer.
For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.
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