Metabolic bone disease: oncogenic osteomalacia: practice question

A Orthopaedics 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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Orthopaedics · Metabolic bone disease: oncogenic osteomalacia

Sample item

A 50-year-old man has progressive bone pain, proximal muscle weakness and pseudofractures. Serum phosphate is low with excessive urinary phosphate loss, calcitriol is low, and there is no family history. A small mesenchymal tumour is found in the soft tissue of the foot. Which mediator causes the syndrome?

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

The answer and the reasoning

A. Fibroblast growth factor 23

Phosphaturic mesenchymal tumours secrete FGF23, which inhibits renal phosphate reabsorption and 1-alpha-hydroxylase. The result is hypophosphataemic osteomalacia that is cured by removing the tumour.

Option by option

  • A. Fibroblast growth factor 23 (correct)

    Correct. Tumour-derived FGF23 causes phosphate wasting and low calcitriol.

  • B. Sclerostin

    Sclerostin inhibits bone formation and does not cause renal phosphate loss.

  • C. Interleukin-6

    Interleukin-6 is involved in inflammation and myeloma bone disease and does not cause phosphate wasting.

  • D. Parathyroid hormone-related peptide

    PTHrP causes hypercalcaemia of malignancy, not hypophosphataemic osteomalacia.

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 Orthopaedics question

What is the answer to this Orthopaedics question?

The best answer is A, Fibroblast growth factor 23. Phosphaturic mesenchymal tumours secrete FGF23, which inhibits renal phosphate reabsorption and 1-alpha-hydroxylase.

Why is "Sclerostin" not the answer?

Sclerostin inhibits bone formation and does not cause renal phosphate loss.

Why is "Interleukin-6" not the answer?

Interleukin-6 is involved in inflammation and myeloma bone disease and does not cause phosphate wasting.

Why is "Parathyroid hormone-related peptide" not the answer?

PTHrP causes hypercalcaemia of malignancy, not hypophosphataemic osteomalacia.

What concept does this question test?

It tests Metabolic bone disease: oncogenic osteomalacia in Orthopaedics. The result is hypophosphataemic osteomalacia that is cured by removing the tumour.

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 Metabolic bone disease: oncogenic osteomalacia?

Pair each fracture with its classic complication and nerve injured. Then use the flashcards and the other Orthopaedics 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.