Graves Postoperative Hypocalcemia

Grave's thyrotoxicosis is initially managed with antithyroid blocking agents, followed by surgery and/or radioiodine therapy. In children if medical therapy fails, total thyroidectomy is the next treatment of choice. Overall the most common complication after total thyroidectomy is hypocalcemia or tetany which occurs with a greater incidence in patients with Graves disease when compared with the same procedure in children with nodular disease or thyroid cancer. Most cases of postop hypocalcemia are transient with less than 5% permanent. Several mechanisms for the development of hypocalcemia in Graves disease after total thyroidectomy are proposed. They include parathyroid hormone (PTH) insufficiency related to injury, devascularization or inadvertent removal of the parathyroid glands. Also, increase release of thyrocalcitonin during gland manipulation. This are not the principal mechanisms of hypocalcemia. The most principal mechanism of hypocalcemia after Graves thyroidectomy is rapid reversal of an osteodystrophy that existed before surgery caused by the elevated thyroid hormone level. Grave's children develop a negative calcium level and loss of bone in the hyperthyroid state something that is partially reversed with antithyroid blocking therapy known as recalcification tetany or hungry bone syndrome. When the excess secretion of hormone is eliminated with surgery the extent of bone restoration will be replenish with calcium hence lowering the ionized calcium blood levels and causing symptoms of tetany. With excess hormone there is reduced calcium bowel absorption in addition to bone resorption due to osteoclast activation and loss of calcium in the urine. Also, antithyroid drug therapy causes calcium and vitamin D deficiency. Twofold increase rate of a negative calcium slope in the first six hours after surgery or very low iPTH levels (< 10 pg/ml) predicts severe hypocalcemia. Risk factors that enhance the state of postop hypocalcemia are younger age and obesity. Preoperative calcium supplementation for Graves children before surgery replenishes calcium body stores and reduces symptomatic hypocalcemia. Teriparatide (PTH 1-34) therapy in post-thyroidectomy patients can control and prevent symptomatic hypocalcemia and reduce hospitalization (THYPOS trial).

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