The Reality of Hypoparathyroidism After Thyroidectomy: Which Risk Factors are Effective? Single-Center Study

One of the most common complications of thyroidectomy is hypoparathyroidism and that complication has a multifactorial etiology. The etiology of post-operative hypoparathyroidism is multifactorial, some factors affecting hypoparathyroidism have been revealed in the literature, and there are some conflicting results about this complication. In the present study, we aimed to evaluate pre-operative and intraoperative factors affecting development of hypoparathyroidism.

Data of 542 patients underwent thyroidectomy±central dissection (±lateral dissection) and whose post-operative parathormone values could be obtained, between 2012 and 2020 were collected prospectively and evaluated retrospectively. A parathyroid hormone (PTH) value of <15 pg/mL at the post-operative 4^th h was defined as hypoparathyroidism, and a calcium (Ca) value of <8 mg/dl on the 1^st post-operative day was defined as biochemical hypocalcemia. Patients were divided into two groups as post-operative hypoparathyroidism (Group 1) and non-hypoparathyroidism (Group 2). In addition, PTH value below the reference value at the post-operative 6^th month and/or still needing calcium treatment was defined as permanent hypoparathyroidism. Demographic data of the patients, pre-operative biochemical values, surgical indications, intraoperative findings, post-operative 4^th h PTH values, post-operative 1^st day calcium values, and pathological examination of the specimen whether there was an unintenionally resected parathyroid gland or not were evaluated as risk factors for hypoparathyroidism. A logistic regression model was used to determine independent risk factors for the development of hypoparathyroidism.

Hypoparathyroidism was determined in 124 (22.9%) and hypocalcemia was determined in 120 (22.1%) patients. According to 6-month follow-up period; 110 (20.3%) patients were transient, 7 (1.3%) patients were permanent, and 7 (1.3%) patients data could not be obtained. The hypocalcemia rate was higher in Group 1 (39.3% vs. 14.3%, p<0.0001), also the post-operative 1st day calcium values were lower (8.2+0.7 mg/dl vs. 8.5+0.6 mg/dl; p=0.000). The rate of parathyroid autotransplantation, the rate of parathyroid gland in pathological specimen, and the rate of central dissection were significantly higher in Group 1 compared to group 2 (15.8% vs. 8%; p=0.006; 20% vs. 10.6%; p=0.003; 16.4% vs. 5.3%, p<0.0001, respectively). The difference between the two groups was significant in terms of the number of remaining parathyroids, and the rate of the number of patients with four remaining parathyroids in place was higher in Group 2 than in Group 1 (84.1% vs. 67.9; p=0.000). In the logistic regression analysis, only central dissection is an independent risk factor affecting the development of hypoparathyroidism, and central dissection increases the risk of hypoparathyroidism approximately 2.3 times (p=0.014; OR: 2.336). The other factors were not determined as independent risk factor.

Performing central neck dissection with total thyroidectomy may increase the risk of hypoparathyroidism development. The risk of hypoparathyroidism should be considered when evaluating the indications and dissection extent in the central dissection. Maximum effort should be made to preserve the parathyroid glands and their vascularization during central dissection, and if there is a removed parathyroid gland, it should be autotransplanted.