Vitamins and minerals: hungry bone syndrome: practice question

A Biochemistry 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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Biochemistry · Vitamins and minerals: hungry bone syndrome

Sample item

Three days after parathyroidectomy for long-standing primary hyperparathyroidism with severe bone disease, a patient has perioral tingling and carpopedal spasm. Serum calcium is 6.8 mg/dL with low phosphate and magnesium, and PTH is within the normal range. What is the mechanism?

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

The answer and the reasoning

D. Rapid deposition of mineral into demineralised bone

After removal of the adenoma, PTH-driven resorption stops while the depleted skeleton avidly takes up calcium, phosphate and magnesium. Calcium may stay low for weeks and needs large supplements with calcitriol. A normal PTH with low phosphate separates it from hypoparathyroidism, where phosphate is high.

Option by option

  • A. Resistance of the intestine to vitamin D

    Intestinal vitamin D resistance does not follow parathyroid surgery.

  • B. Excess calcitonin from C cells

    Calcitonin excess does not cause clinically significant hypocalcaemia.

  • C. Autoimmune destruction of the remaining parathyroids

    Loss of parathyroid function would give a low PTH and a high phosphate.

  • D. Rapid deposition of mineral into demineralised bone (correct)

    Correct. Avid skeletal uptake of mineral lowers calcium, phosphate and magnesium together, with preserved PTH.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Rapid deposition of mineral into demineralised bone. After removal of the adenoma, PTH-driven resorption stops while the depleted skeleton avidly takes up calcium, phosphate and magnesium.

Why is "Resistance of the intestine to vitamin D" not the answer?

Intestinal vitamin D resistance does not follow parathyroid surgery.

Why is "Excess calcitonin from C cells" not the answer?

Calcitonin excess does not cause clinically significant hypocalcaemia.

Why is "Autoimmune destruction of the remaining parathyroids" not the answer?

Loss of parathyroid function would give a low PTH and a high phosphate.

What concept does this question test?

It tests Vitamins and minerals: hungry bone syndrome in Biochemistry. Calcium may stay low for weeks and needs large supplements with calcitriol. A normal PTH with low phosphate separates it from hypoparathyroidism, where phosphate is high.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Vitamins and minerals: hungry bone syndrome?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.