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Retired NBME 20 Answers

nbme20/Block 1/Question#36 (reveal difficulty score)
A 56-year-old man is admitted to the hospital ...
Rhabdomyolysis ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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submitted by โˆ—hayayah(1212)
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Rhabdomyolysis can present looking like a kidney injury (it can lead to acute tubular necrosis as well). The electrolyte findings are just like renal failure (Inc. K+, inc. PO4-, dec. Ca)

To differentiate between rhabdomyolysis and kidney injury, you check the urine to see if there are any RBCs. In rhabdomyolysis there are no free RBCs in the urine.

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ergogenic22  "Crush injury" is a buzz word for rhabdo +18
ibestalkinyo  The mechanism by which AKI occurs after rhabdomyolysis are due to free radical formation. Other urine finding include blood on dipstick, but as hayayah said, no frank RBCs. +3
skonys  I hadrhabdo and fat emboli and chose fat emboli because fracture of both legs (long bones). I understand that rhabdo is also implied as its a crush injury so damage to the overlying muscles would be present. But would the renal symptoms of fat embolus be different? Or is it just that fat emboli usually throw clots to the brain and not kidneys bilaterally. +2
plaguedbyspleen  Exactly, I think renal failure due to fat embolism would be extremely rare. Recall the textbook triad for fat embolism is hypoxemia, neuro abnormalities, and petechial rash and we don't see any of those in this stem. Also crush injury makes me think that the lower extremities are a total mess compared to what we would see with a mid-femur fracture, but that is just me pondering. +



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submitted by โˆ—doso2222(12)
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Crush injury --> Rhabdomyolysis --> Muscle cells release myoglobin, urate, phosphate, purines --> precipitation at DCT --> tubular obstruction --> oliguria, hyperkalemia and increased BUN.

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