Preoperative imaging predicts change in bone mineral density after parathyroidectomy for primary hyperparathyroidism.

Abstract

Bone Mineral Density (BMD) improves after parathyroidectomy (PTX), but data on factors that predict bone recovery are limited. No studies have evaluated if preoperative imaging findings are associated with postoperative change in BMD. We hypothesized that larger, metabolically active glands would be associated with greater increase in BMD after PTX. Patients with primary hyperparathyroidism (PHPT) who underwent combined Tc-99m sestamibi and 4D-CT imaging prior to PTX and had pre- and post-operative dual-energy X-ray absorptiometry (DXA) at our institution were considered for inclusion. Retrospectively, data were collected from imaging studies on each parathyroid gland, including estimated weight (using the ellipsoid formula) and contrast enhancement on 4D-CT as well as sestamibi avidity. Total estimated parathyroid weight was calculated. The main outcome measure was the percent change in BMD at the lumbar spine (LS) from pre- to post-operative DXA. Predictors of change in BMD at the LS were assessed. Complete DXA data was available in 25 patients. Median total parathyroid weight on 4D-CT was 270mg, and mean change in BMD at the LS was 2.4±4.3%. The increase in BMD was best predicted by higher preoperative serum calcium (p=0.01), greater estimated parathyroid weight (p=0.001), sestamibi avidity (p=0.03), and increased time between DXA scans (p=0.03) in the multivariable model (R2=0.79, p<0.0001). In PHPT, higher preoperative serum calcium, parathyroid gland weight on imaging, and sestamibi avidity are associated with greater increases in BMD after curative PTX. These findings suggest that larger, metabolically active adenomas may mobilize more calcium from bone.