Patients who undergo thyroid surgery, especially those who undergo radical bilateral thyroid cancer resection for bilateral thyroid lesions, sometimes experience hand numbness, facial numbness or leg cramps after surgery. This is a sign of low blood calcium. So how is it caused? This requires us to start from the anatomy of the parathyroid glands and their physiological functions. The parathyroid glands are two pairs of small endocrine glands located behind the thyroid gland, two on one side, like four small beans, each gland is 3-8 mm long, 2-5 mm wide and 0.5-2 mm thick. the total weight of the four glands is no more than 0.3 g. Although the glands are small, they function as a small body. Although the glands are small, their function is quite large. The parathyroid glands secrete parathyroid hormone, whose physiological function is to regulate calcium metabolism in the body and maintain the balance of calcium and phosphorus. Once parathyroid hormone is not secreted enough, the blood calcium level drops sharply, leading to muscle spasms, hand and leg cramps, facial numbness and other low blood calcium manifestations. Laboratory tests reveal a decrease in calcium and parathyroid hormone in the blood. So why do patients with thyroid surgery, especially those who have had bilateral thyroidectomy (bilateral thyroid cancer), have low calcium? This has to be analyzed. One reason is that the parathyroid glands had to be removed because the tumor had invaded the parathyroid glands. In one case, the parathyroid glands were not removed, but the blood supply to the parathyroid glands was affected by the severance of the ligated vessels (mainly the inferior thyroid artery) during the surgical removal of the thyroid glands. So what happens when hypoparathyroidism and hypocalcemia occur? It can be resolved with oral calcium preparations, preferably oral calcium tablets containing vitamin D, as calcium absorption depends on the assistance of vitamin D. Follow up closely for blood calcium and parathyroid hormone. If parathyroid hormone is still low after about six months, it means that the parathyroid glands may have been surgically removed or parathyroid function can no longer be restored, in which case you need to take calcium tablets for life. If the parathyroid hormone is normal again, it means that the parathyroid glands have started to secrete again due to the growth of the collateral circulation, so stop using calcium tablets for a period of time, and if no more low calcium symptoms appear, then you can stop taking calcium tablets completely.