Gastroenterology: Crohn disease and nephrolithiasis: practice question

A General Medicine question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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General Medicine · Gastroenterology: Crohn disease and nephrolithiasis

Sample item

A 28-year-old man with long-standing terminal ileal Crohn disease and an intact colon has steatorrhoea. He presents with colicky flank pain and haematuria, and imaging shows a renal calculus. Which stone type is most likely?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Calcium oxalate

In ileal disease, unabsorbed fatty acids bind intestinal calcium, leaving oxalate free to be absorbed by the colon (enteric hyperoxaluria), and this leads to calcium oxalate stones. Treatment includes a low-oxalate, low-fat diet, oral calcium with meals and fluids. Uric acid stones are more typical of ileostomy patients with dehydration and acidic urine.

Option by option

  • A. Calcium oxalate (correct)

    Enteric hyperoxaluria from fat malabsorption causes calcium oxalate stones.

  • B. Cystine

    Cystine stones arise from the inherited tubular disorder cystinuria.

  • C. Struvite (magnesium ammonium phosphate)

    Struvite stones follow urease-producing urinary infections such as Proteus.

  • D. Uric acid

    Uric acid stones are seen with volume depletion and acidic urine, as in ileostomy, not with an intact colon and fat malabsorption.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this General Medicine question

What is the answer to this General Medicine question?

The best answer is A, Calcium oxalate. In ileal disease, unabsorbed fatty acids bind intestinal calcium, leaving oxalate free to be absorbed by the colon (enteric hyperoxaluria), and this leads to calcium oxalate stones.

Why is "Cystine" not the answer?

Cystine stones arise from the inherited tubular disorder cystinuria.

Why is "Struvite (magnesium ammonium phosphate)" not the answer?

Struvite stones follow urease-producing urinary infections such as Proteus.

Why is "Uric acid" not the answer?

Uric acid stones are seen with volume depletion and acidic urine, as in ileostomy, not with an intact colon and fat malabsorption.

What concept does this question test?

It tests Gastroenterology: Crohn disease and nephrolithiasis in General Medicine. Treatment includes a low-oxalate, low-fat diet, oral calcium with meals and fluids. Uric acid stones are more typical of ileostomy patients with dehydration and acidic urine.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Gastroenterology: Crohn disease and nephrolithiasis?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.