SUN-766 - When Calcium Isn'T Enough: Syncope, Long QT, and Extreme Supplement Needs after Thyroidectomy

Background: Post-thyroidectomy hypocalcemia is the most common complication after total thyroidectomy and usually resolves as parathyroid function recovers. A subset of patients develops prolonged, difficult-to-taper hypocalcemia requiring high-dose calcium and calcitriol for months, increasing risk for recurrent symptoms, syncope, and QTc prolongation. Escalation of therapy including PTH replacement may be considered when symptoms recur with down-titration or supplementation needs are extreme.
Clinical

Case: A 34-year-old woman with Hashimoto’s thyroiditis underwent total thyroidectomy with right inferior parathyroidectomy for papillary thyroid carcinoma. One week postoperatively, she presented with nausea, vomiting, paresthesias, and syncope. Total calcium was 7.9 mg/dL (corrected calcium 8.1 mg/dL), followed by a nadir calcium of 6.8 mg/dL; ionized calcium was 4.1 mg/dL with low intact PTH 7.3 pg/mL. She improved after IV calcium gluconate and was discharged on calcitriol plus oral calcium. Attempts to taper calcium repeatedly triggered immediate paresthesias. Over subsequent months, intact PTH remained persistently low at 6 to 8.7 pg/mL on serial checks. Months later, after missing one calcitriol dose, she developed extremity tingling followed by altered mental status and syncope; total calcium was 7.8 mg/dL (corrected calcium 7.5 mg/dL) and QTc was prolonged to 499 ms. She required multiple doses of IV calcium gluconate and was discharged on increased calcitriol and high-dose calcium carbonate (8 g/day). She later experienced exertion-associated paresthesias and syncope while hiking without access to calcium tablets; she did not seek emergency care and resumed high-dose supplementation. Serum calcium checked several days later was 9.4 mg/dL (corrected calcium 9.0 mg/dL). She currently remains on calcitriol 0.25 mcg twice daily and calcium carbonate 4 g three times daily (12 g/day), with recurrence of symptoms when attempting dose reduction. She is considering PTH replacement therapy due to persistent symptom burden and extreme supplementation requirements.

Conclusion: This case demonstrates a high-severity course of postsurgical hypoparathyroidism marked by recurrent syncope, neurocognitive symptoms, and QTc prolongation months after thyroidectomy, with persistent biochemical hypoparathyroidism and functional dependence on high-dose calcium and calcitriol to maintain stability. The patient relapsed quickly with down-titration and had recurrent triggers, including missed calcitriol and exertion without ready supplementation. This highlights the need for proactive outpatient action plans and close monitoring, with timely escalation of therapy including consideration of PTH replacement when conventional regimens fail to prevent clinically consequential episodes.

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