Step 1

Musculoskeletal 2

A 55-year-old man presents to the emergency department because he fell on his left arm two hours ago and believes it is broken. He states that his left arm and back have been aching for the past six weeks, so he has been taking acetaminophen daily. The rest of his past medical history is unremarkable. Physical examination reveals swelling and tenderness to palpation over the left upper arm. Distal pulses and sensation are intact. Radiographs of the left humerus show that the left humerus is bright white and wider than the right, bowed, and has a fracture that goes straight through horizontally with no chipping. Laboratory tests show elevation of serum alkaline phosphatase with serum calcium and serum phosphate in normal ranges. A histological sample of the bone shows a bizarre jigsaw pattern.

Which of the underlying mechanisms is the cause for the patient's presentation?

  • A) EWSR1 gene mutation resulting in cells expressing high levels of CD99
  • B) Gene mutation causing an increase in NFkB
  • C) Gene mutation causing a decrease in NFkB
  • D) Inactivation of p53 and Rb leading to malignant osteoid deposition
  • E) Malignant giant cells expressing RANKL

Authors

Carleigh VanDenBrook

Editor

Dr. Ted O'Connell

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