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NBME 22 Answers

nbme22/Block 2/Question#3

A previously healthy 28-year-old man comes to the ...

Nephrolithiasis

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submitted by hopsalong(3),

This question has a lot of answer options, and you arrive at Nephrolithiasis by throwing out all the other options by what is missing.

A, B - Cortical Necrosis and Papillary Necrosis almost always occur in the setting of ischemia. Previously healthy 28 year old man has no evidence of significantly decreased renal perfusion.

C - Acute Tubular Necrosis is what you should think of with Salicylate (NSAID) toxicity. There are many other nephrotoxic drugs that cause ATN, but think of ATN as drug induced kidney damage.

D - Cystitis - Flank pain is related to kidney injury, not bladder damage. Cystitis could be possible in ascending UTI, but the patient has no fever and is male (much less common in males).

E - Glomerulonephritis - This gets into nephrotic/nephritic syndromes. The stem mentions that he has blood in the urine which may lead you down the nephritic pathway, but he does not have any of the other associated symptoms.

F - Hypernephroma - Another word for Renal Cell Carcinoma. No weight loss or other cancer related symptoms (fatigue etc.)

G - Interstitial Nephritis - This is often a drug induced IMMUNE mediated nephrotoxicity. This is a type IV hypersensitivity reaction that occurs weeks to months after the start of medication (like NSAIDs). ATN is more associated with drug overdose while Interstitial is more associated with immune reaction. Intersitial Nephritis will have WBC casts in urine.

I - Pyelonephritis - Caused by ascending UTI but no fever is present.

This leaves Nephrolithiasis (H) as the correct answer. 85% of Nephrolithiasis is associated with hypoactive bowel sounds. The pain for nephrolithiasis can relapse and remit, and occasionally the pain can travel from the kidney (flank pain) to the scrotum as the stone moves through the ureter.

whoissaad  Great explanation. Always found it hard to differentiate between ATN and AIN due to NSAID use. This made it clear. Thanks! +1  
hyperfukus  yasss +