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Tumour-induced osteomalacia — SCE Endocrinology MCQ

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HardCalcium/BoneTumour-induced osteomalaciaSCE Endocrinology

A 51-year-old man has recurrent fractures, bone pain and muscle weakness. Phosphate is 0.42 mmol/L, calcium is normal, ALP is raised, 1,25-dihydroxyvitamin D is inappropriately low and FGF23 is elevated. PET-CT shows a small thigh soft-tissue lesion. What is the underlying pathophysiology?

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Correct answer: B — FGF23-mediated renal phosphate wasting from a mesenchymal tumour

Tumour-induced osteomalacia is caused by FGF23 secretion, leading to renal phosphate wasting and impaired calcitriol production. PTH excess would not produce high FGF23 with this pattern. The pearl is that curing the tumour can cure the osteomalacia.

Reference: Endocrine Society hypophosphataemia guidance