Parathyroidectomy for Normocalcemic Primary Hyperparathyroidism is Associated with Improved Bone Mineral Density Regardless of Postoperative Parathyroid Hormone Levels

Background: Biochemical cure in normocalcemic primary hyperparathyroidism (nPHPT) is defined as parathyroid hormone (PTH) level normalization 6 months after parathyroidectomy. However, recent studies show that a significant number of nPHPT patients have persistent PTH elevation postoperatively. We sought to correlate changes in PTH levels with skeletal outcomes after parathyroidectomy in nPHPT patients. Methods: Adult patients who underwent parathyroidectomy at a tertiary referral center for sporadic PHPT between 2010 and 2020 were reviewed. Pre- and postoperative (6 months, 18 months, and last follow-up) laboratory and bone mineral densities (BMD) were recorded. Primary outcome was 18-month postoperative BMD change in the lumbar spine (LS), total hip (TH) and femoral neck (FN) in normocalcemic and hypercalcemic PHPT (hPHPT) patients. Results: Of 661 patients included, 68 had nPHPT. nPHPT patients frequently had multigland disease (31% vs. 18%, p = 0.014), more bilateral cervical explorations (22% vs. 13%, p = 0.042), and fewer achieved biochemical cure (76% vs. 95%, p < 0.001) than hPHPT patients. Twenty-eight nPHPT patients had BMD data for comparison. Overall, nPHPT patients had improvement in the LS (1.84%, p = 0.002) and TH (1.64%, p = 0.014). When stratified by postoperative PTH levels, nPHPT patients with persistent PTH elevation had more BMD improvement at the TH than those who normalized PTH (3.73% vs. − 0.83%, p = 0.017). There was no difference in improvement at the LS or FN (p = NS). Conclusion: Parathyroidectomy is associated with improved BMD in nPHPT patients with bone disease. Although one in four nPHPT patients had elevated postoperative PTH levels persisting throughout the study, BMD improvement was still seen regardless of postoperative PTH level normalization.