Background and Aims: Surgery plays an important role in the treatment of thyroid disease, and hypoparathyroidism is one of the common complications of thyroid surgery. However, different kinds of thyroid pathologies have different indications for different types of thyroid surgery, which may exert different impacts on parathyroid function. This study was conducted to investigate the differential influences of different types of thyroid surgery on parathyroid function and analyze the reasons. 
Methods: The clinical data of 319 eligible patients who underwent thyroid surgeries from April 2017 to March 2019 were retrospectively analyzed. Of the patients, 111 cases underwent unilateral thyroid lobectomy (unilateral resection group), 107 cases underwent bilateral thyroid lobectomy (bilateral resection group), 71 cases underwent bilateral thyroid lobectomy with central lymph node dissection (bilateral resection plus level VI dissection group), and 30 cases underwent bilateral thyroid lobectomy with central and lateral neck dissection (bilateral resection plus level II–VI dissection group). During the operation, 1-2 points on the capsule around the affected side close to the isthmic region were selected, and 0.1-0.2 mL of nanocarbon suspension was injected at each point. Meticulous capsular dissection technique was adopted in all patients for in-situ preservation of the parathyroid glands. If the parathyroid glands failed to be retained in situ, they were immediately cut into pieces or homogenates and reimplanted into the sternocleidomastoid muscle. The changes in parathyroid hormone (PTH) and blood calcium levels before and after surgery as well as the incidence rates of postoperative hypoparathyroidism and hypocalcemia among groups of patients were observed and compared.
Results: The preoperative general data and PTH and blood calcium levels showed no significant differences among groups (all P>0.05). After surgery, both PTH and blood calcium levels were significantly decreased in all groups compared with their preoperative levels (all P<0.01), but their decreasing amplitudes were significantly magnified with the expansion of surgical scope, namely unilateral resection group < bilateral resection group < bilateral resection plus level VI dissection group < bilateral resection plus level II–VI dissection group, and all differences had statistical significance (all P<0.05). The incidence rates of hypoparathyroidism and hypocalcemia were likewise increased with the expansion of surgical scope, and in unilateral resection group, bilateral resection group, bilateral resection plus level VI dissection group and bilateral resection plus level II–VI dissection group, the incidence of hypoparathyroidism was 9.9%, 32.7%, 56.3% and 73.3%, and the incidence of hypocalcemia was 0, 1.9%, 19.7% and 50.0%, respectively. Follow-up was conducted for 24 weeks in all patients, and no permanent hypoparathyroidism was noted.
Conclusion: All kinds of thyroid surgery have certain impacts on the parathyroid function, and the possibility of parathyroid injury and risk of the occurrence of hypoparathyroidism will increase with the expansion of the surgical scope. So, the protective measures for parathyroid glands should be adopted in all thyroid surgeries, with meticulous dissection and reduced interference in the blood supply of the parathyroid glands, and thereby to decrease the incidence of hypoparathyroidism as far as possible.