K. M. Ritter1, D. Elfenbein1, D. F. Schneider1, H. Chen1, R. S. Sippel1 1University Of Wisconsin,Division Of General Surgery, Department Of Surgery,Madison, WI, USA
Introduction: Parathyroid hormone (PTH) levels are often measured after thyroid surgery and can be used to detect patients at risk for postoperative hypoparathyroidism. The goals of this study were to elucidate the time course of parathyroid gland function recovery and to determine the incidence of permanent hypoparathyroidism.
Methods: Patients who underwent a total or completion thyroidectomy from 1/2006 to 12/2013 were identified from a retrospective review of a prospectively collected institutional database. Low PTH was defined as a PTH measurement <10 pg/mL immediately after surgery. Patients were followed for 1 year. Recovery of parathyroid gland function was defined as PTH ≥10 pg/mL and no need for therapeutic calcium or activated vitamin D (calcitriol) supplementation to prevent hypocalcemic symptoms. Patients were considered to be permanently hypoparathyroid if they had not recovered within 1 year. Multivariate logistic regression modeling was performed to identify independent risk factors for a low postoperative PTH and for permanent hypoparathyroidism.
Results: Of 1054 total thyroidectomy patients, 189 (18%) had postoperative PTH <10 pg/mL. Of those 189 patients, 132 (70%) showed resolution within 2 months of surgery, a third (n=49) of which had resolved within 1-2 weeks of surgery. Of the 57 patients with hypoparathyroidism at 2 months, 49% resolved by 6 months after surgery and an additional 16% resolved by 1 year. At 1 year, 20 patients were considered to have permanent hypoparathyroidism due to the need for ongoing supplementation. Surprisingly, 50% of those patients had recovery of PTH levels to ≥10 pg/mL yet still required supplementation to avoid symptoms. The permanently hypoparathyroid group represents 11% of patients with initial postoperative PTH <10 pg/mL and 2% of the entire cohort. On multivariate analysis, independent risk factors for low postoperative PTH included parathyroid autotransplantation (OR = 2.6; 95% CI, 1.8-3.8) and the presence of parathyroid tissue on final pathology report (OR = 2.2; 95% CI, 1.5-3.3). The only independent risk factor for permanent hypoparathyroidism was parathyroid tissue on pathology report (OR = 3.6, 95% CI, 1.1-11.5). Interestingly, age, gender, neck dissection, thyroiditis, and malignancy were not independently associated with low postoperative PTH or permanent hypoparathyroidism.
Conclusion: Low PTH is a common occurrence after thyroid surgery, but the vast majority of patients showed parathyroid gland function recovery within 2 months of surgery. Notably, 5% of patients with low postoperative PTH resolved 6-12 months after surgery, suggesting that 12 months may be the most appropriate time point for defining hypoparathyroidism as permanent.
