If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 2 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.  

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A 72-year-old woman comes to the physician because of a three-day history of mid-back pain. She denies any trauma to the back. Examination shows point tenderness over the T8 vertebra.

Laboratory studies show:

  • Hemoglobin: 13 g/dL.
  • Na+: 137 mEq/L.
  • Cl: 101 mEq/L.
  • K+: 4.3 mEq/L.
  • HCO3: 25 mEq/L.
  • Urea nitrogen (BUN): 21 mg/dL.
  • Creatinine: 0.71 mg/dL.
  • Albumin: 3.6 g/dL.
  • Ca+: 9.0 mg/dL.
  • Alkaline phosphatase: 50 U/L.

X-ray of the spine shows a compression fracture of the T8 vertebral body. Dual energy x-ray absorptiometry (DEXA) shows a bone mineral density T-score of -2.7.

Which of the following is the most likely diagnosis?

A. Metastatic disease.

B. Multiple myeloma.

C. Osteomalacia.

D. Osteopenia.

E. Osteoporosis.

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The correct answer is E.

In this patient—a 72-year-old female with an acute, atraumatic thoracic vertebral compression fracture confirmed on X-ray, with a T-score of -2.7 on her DEXA scan—the most likely diagnosis is osteoporosis.

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Choices A and B: Multiple myeloma and metastatic disease should be included in the differential diagnosis when evaluating older adults with non-traumatic vertebral fractures. Findings in multiple myeloma include laboratory abnormalities, such as elevated serum calcium and creatinine levels, and constitutional symptoms such as weight loss.

In this case, the laboratory evaluation is normal, supporting the diagnosis of an osteoporotic compression fracture. Metastatic lesions to bone can lead to pathologic fractures. This patient does not have a history of previously diagnosed cancer nor systemic symptoms which would lead to the suspicion of underlying cancer.

Choice C: Osteomalacia is the result of a reduction in the mineral content of bone with a normal bone matrix. Osteomalacia is caused by vitamin D deficiency, hypophosphatemia, gastrectomy, and kidney diseases. This is less likely in this patient with normal laboratory values and no other symptoms.

Choice D: Osteopenia is characterized by a bone mineral density T-score that is 1 to 2.5 standard deviations below the mean. It is the intermediate between normal bone and osteoporosis.

    • Bone mineral density T-score <-2.5 is diagnostic of osteoporosis.
    • Osteoporosis may present with vertebral compression fractures.

For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.

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