Two days after parathyroidectomy for severe primary hyperparathyroidism, a patient's serum calcium falls to 6.2 mg/dL with phosphate 1.6 mg/dL, requiring large continuous calcium infusions. PTH is now appropriately elevated. What explains the persistent hypocalcemia?

• A Recurrent laryngeal nerve injury impairing calcium sensing
• B Permanent surgical destruction of all remaining parathyroid tissue
• C Hungry bone syndrome: avid remineralization of chronically depleted bone sequestering calcium and phosphate ✓
• D FGF23 surge from osteocytes causing renal phosphate retention

Explanation

After removal of a PTH-secreting adenoma, the previously resorbed skeleton rapidly takes up calcium and phosphate during remineralization, producing profound hypocalcemia termed hungry bone syndrome. Elevated phosphate argues against residual hyperparathyroidism, and the appropriately rising PTH indicates functioning remaining glands rather than surgical hypoparathyroidism. FGF23 promotes phosphate wasting, not retention, so it cannot explain the findings.

Reference: Williams Textbook of Endocrinology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.