A 35-year-old man undergoes total thyroidectomy for papillary thyroid carcinoma (1.8 cm, N1a, M0). Postoperatively, he develops carpopedal spasm and a positive Chvostek sign. Serum calcium is 7.0 mg/dL. The pathophysiology of the hypocalcemia is most accurately explained by:
- A Hungry bone syndrome due to pre-existing hyperthyroidism
- B Disruption of parathyroid blood supply causing hypoparathyroidism ✓
- C Dilutional hyponatremia post-surgery
- D Elevated calcitonin from residual C cells
Correct answer: B. Disruption of parathyroid blood supply causing hypoparathyroidism
Explanation
Post-thyroidectomy hypocalcemia results from inadvertent removal of parathyroid glands or injury to their blood supply (inferior thyroid artery branches), causing hypoparathyroidism. Transient hypoparathyroidism occurs in up to 30% of total thyroidectomies; permanent hypoparathyroidism in 1-2%. Hungry bone syndrome occurs after parathyroid surgery (parathyroidectomy for primary hyperparathyroidism) when bones rapidly sequester calcium. Calcitonin does not cause symptomatic hypocalcemia. Management includes IV calcium gluconate acutely and oral calcium with calcitriol.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
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