Predictors of Bone Mineral Density Improvement in Patients Undergoing Parathyroidectomy for Primary Hyperparathyroidism

Primary hyperparathyroidism (PHPT) results in increased bone turnover, resulting in bone mineral density (BMD) reduction and a predisposition towards fractures. Parathyroidectomy (PTX) is the only definitive cure. The primary goals of this study were to investigate the impact of PTX on BMD in patients with PHPT and to identify factors associated with post-operative BMD improvement using a multivariate model. Between 1999 and 2010, a total of 757 patients underwent PTX for treatment of PHPT; 123 patients had both a pre- and a post-operative dual-energy X-ray absorptiometry (DEXA) scan. A prospective database was queried to obtain information about patient demographics, medications, comorbidities, and pre- and post-operative laboratory values. A Cox regression model was used to stratify patients and to identify factors that independently predict BMD response following PTX in this patient population. Overall, mean percent change in BMD was +12.31 % at the spine, +8.9 % at the femoral neck (FN), and +8.5 % at the hip, with a mean follow-up of 2.3 +/- A 1.5 years. A total of 101 (82.1 %) patients had BMD improvement at their worst pre-operative site. In patients who improved, 69.9 % (n = 86) had > 5 % increase. Factors associated with BMD improvement at the worst pre-operative site were as follows: male gender (hazard ratio [HR] 2.29; 95 % confidence interval [CI] 1.54-4.21); pre-operative BMD with T-score less than -2.0 (HR 1.89; 95 % CI 1.11-2.39); age < 55 years (HR 1.74; 95 % CI 1.14-2.25); BMD DEXA scan at > 2.5 years post-operatively (HR 1.71; 95 % CI 1.09-2.17); history of previous fracture (HR 1.24; 95 % CI 1.05-1.92); and private insurance (HR 1.18; 95 % CI 1.06-2.1). The use of bisphosphonates, estrogens, vitamin D supplementation, or tobacco; obesity; history of previous PTX, serum calcium or parathyroid hormone levels were not independently associated with post-operative BMD improvement. Osteoporosis is one of the established National Institutes of Health criteria for PTX in asymptomatic patients with PHPT, but BMD improvement is not consistently seen during the post-operative period. Gender, age, more severe pre-operative bone disease, and insurance status were all predictors for greater BMD improvement following PTX. Further studies with a rigorous post-operative BMD regimen are needed in order to validate these results.