Applicability of Intraoperative Parathyroid Hormone Assay During Total Thyroidectomy as a Guide for the Surgeon to Selective Parathyroid Tissue Autotransplantation

Abstract

Intraoperative parathyroid hormone assay (IOPTH) has been suggested to have value in predicting the development of postoperative hypoparathyroidism after thyroid surgery. IOPTH has been validated in identification of patients at risk of postoperative hypocalcemia requiring early onset of calcium supplementation therapy and in improving selection of patients eligible for a safe early discharge. However, the value of IOPTH has not been assessed in a randomized study as a guide for the surgeon to parathyroid tissue autotransplantation (PA). The objective of this study was to evaluate the applicability of IOPTH in guiding the surgeon to selective parathyroid tissue autotransplantation during total thyroidectomy (TT). Between January 2005 and December 2005, 340 patients qualified for total thyroidectomy (TT) who met the inclusion criteria were randomized to two equal-sized groups (n=170): group A, in which elective PA of at least one parathyroid gland was performed in all cases without IOPTH as a guide; and group B, in which selective IOPTH-guided PA was performed, if only the iPTH plasma level was <10 ng/L at 10-20 min after TT (before skin closure). The standard technique of PA consisting of implanting the parathyroid tissue into 10-20 sternocleidomastoid muscle pockets was used in both groups. IOPTH measurements were performed by the STAT-Intraoperative-iPTH-Assay. Serum calcium was routinely monitored at 4, 12, 24, 48, and 72 hr postoperatively. The incidence and severity of hypocalcemia and related symptoms were matched with the IOPTH results. On follow-up, serum calcium and plasma iPTH values were measured at 1, 3, and 6 months postoperatively. The primary end point was the success rate in preventing permanent postoperative hypoparathyroidism. The secondary end point was the use of postoperative medication for transient hypocalcemic symptoms. Twenty-one group B patients (12.3%) had plasma iPTH levels<10 ng/L at 10-20 min after TT (before skin closure) and they underwent selective IOPTH-guided PA. None of the patients from both groups experienced permanent postoperative hypoparathyroidism. Transient postoperative hypocalcemia occurred in 22.3% vs. 11.2% of patients (group A vs. B, respectively; p<0.05). The mean cumulated serum calcium values were significantly lower for group A vs. group B patients within the entire 3-month period after TT (2.12+/-0.09 mmol/L vs. 2.27+/-0.05 mmol/L, respectively; p<0.001). The mean oral calcium supplementation was significantly higher for group A vs. group B patients during the 3 months after TT (2.7+/-0.9 g/day vs. 0.9+/-0.4 g/day, respectively; p<0.001). IOPTH offers valuable information during TT, correctly identifying patients at risk of postoperative hypocalcemia. Selective IOPTH-guided PA in patients with plasma iPTH levels<10 ng/L at 10-20 min after TT reduces the risk of permanent postoperative hypoparathyroidism to zero, and this approach seems to be as effective as elective PA of at least one parathyroid gland without IOPTH guidance. Moreover, selective IOPTH-guided PA significantly decreases the incidence of transient postoperative hypoparathyroidism and the need for calcium supplementation therapy compared with elective PA without IOPTH.