Two days after total parathyroidectomy for severe secondary hyperparathyroidism, a dialysis patient develops carpopedal spasm with calcium 6.2 mg/dL, phosphate 2.0 mg/dL, and alkaline phosphatase 900 U/L. What is the underlying mechanism?
- A Residual parathyroid tissue secreting calcitonin
- B Surgical injury to the recurrent laryngeal nerve causing hyperventilation
- C Rapid uptake of calcium and phosphate by severely depleted bone after removal of the PTH drive ✓
- D Vitamin D toxicity from preoperative calcitriol therapy
Correct answer: C. Rapid uptake of calcium and phosphate by severely depleted bone after removal of the PTH drive
Explanation
Hungry bone syndrome follows parathyroidectomy in patients with severe, long-standing hyperparathyroidism. Sudden withdrawal of PTH unmasks profound skeletal mineral deficit, so osteoblasts avidly take up calcium and phosphate, producing hypocalcaemia, hypophosphataemia, and marked alkaline phosphatase elevation. Recurrent laryngeal nerve injury causes hoarseness, not hypocalcaemia.
Reference: Williams Textbook of Endocrinology, 14th ed.
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