Intraoperative parathormone monitoring to predict operative success in patients with normohormonal hyperparathyroidism

BACKGROUND: It is unclear whether parathyroidectomy guided by intraoperative parathormone (PTH) monitoring is predictive of operative success in patients with normohormonal hyperparathyroidism (nhHPT), a variant of primary hyperparathyroidism (pHPT) in which patients develop clinical manifestations similar to those of pHPT. This study examined intraoperative PTH monitoring in patients undergoing parathyroidectomy for nhHPT. METHODS: We performed a retrospective review of prospectively collected data from adult (age > 18 yr) patients who underwent parathyroidectomy for pHPT at 1 of 2 North American medical centres (in Calgary, Alberta, Canada, or Miami, Florida, United States) between 2007 and 2015. In patients with nhHPT, we used the criterion of an intraoperative decrease of more than 50% in PTH after abnormal gland excision. We defined operative success as continuous eucalcemia more than 6 months after parathyroidectomy. RESULTS: Of 333 patients, 38 (11.4%) had nhHPT, with mean preoperative calcium and PTH levels of 2.7 mmol/L and 53 pg/dL, respectively. An intraoperative decrease of more than 50% in PTH level was seen in 27 patients (71.0%) with nhHPT and 265 patients (89.8%) with classic pHPT at 5 minutes (p < 0.001); the corresponding values at 20 minutes were 35 (92.1%) and 286 (96.9%). Although 5 patients (13.2%) with nhHPT did not reach this criterion until 20 minutes, the rate of operative success was still 97.0% at long-term follow-up (mean 13 mo, range 6–67 mo). Of the 38 patients, 3 (7.9%) did not have an intraoperative decrease of more than 50% in PTH level by 20 minutes. Two of the 3 achieved operative success and remained normocalemic, and 1 developed recurrent disease at 12 months. CONCLUSION: Parathyroidectomy guided by intraoperative PTH monitoring accurately predicted operative success in patients with nhHPT. Intraoperative PTH monitoring may also help identify multiglandular disease in patients with nhHPT, using criteria similar to those in classic pHPT, with comparable operative success.