MON-778 Optimal Timing of Denosumab with Parathyroidectomy in the Setting of Primary Hyperparathyroidism

Abstract Disclosure: R.S. MacLeod: None. S.K. Majumdar: None. Introduction: Primary hyperparathyroidism should be considered in patients with elevated PTH once secondary causes like vitamin D deficiency and calcium malabsorption are corrected. Optimal timing of denosumab therapy surrounding parathyroid surgery to avoid hypocalcemia and rebound resorption is not well described. Case: A 62-year-old woman with history of psoriasis, Grave’s disease, SLE, and angioedema was evaluated for steroid-induced osteoporosis. She had difficulty controlling her symptoms with steroid-sparing agents, needing 20-60mg of daily prednisone for 2 years. She started alendronate, calcium citrate, and high dose ergocalciferol prior to presenting to endocrinology. A follow-up DXA scan 4 years from baseline (prior to initiating steroids) showed stable osteopenia in the lumbar spine and total hip with T-scores of -1.1 and -2.2, respectively. However, the femoral neck T-score was -3.0 indicating osteoporosis and significant worsening of BMD by 15.4% since baseline. Due to worsening of her DXA while on alendronate and continued glucocorticoid therapy, denosumab was initiated for anti-resorptive therapy. Poor absorption of calcium, vitamin D, and alendronate were thought to contribute to osteoporosis and supposed secondary hyperparathyroidism—PTH 118.7 (15-65) pg/mL, calcium 9.8 (8.8-10.2) mg/dL. She remained on prednisone for 3 additional years while on denosumab. A follow up DXA scan after this period showed lumbar spine T-score of -0.9, total hip T-score of -2.0, and femoral neck T-score of -2.8 with all sites showing non-significant increases in BMD, indicating stabilization. Routine labs showed normalization of serum vitamin D 25-OH levels at 40.7 (30-50) ng/mL with continued PTH elevations (between 69-178 pg/mL) and intermittent hypercalcemia (range 10.0-11.4 mg/dL). It was determined that what was thought to be secondary hyperparathyroidism was now consistent with primary hyperparathyroidism. A 4D CT scan of the neck identified a parathyroid adenoma, and she was referred for parathyroidectomy. Outcome and Conclusion: Parathyroidectomy was scheduled in proximity to the next denosumab dose since timing is important due to rebound resorption phenomenon and increased risk of vertebral fractures after delayed or missed denosumab doses. However, peri-procedural hypoparathyroidism and severe hypocalcemia can result if potent anti-resorptive therapy prevents liberation of calcium from bone. Considering this, denosumab was given 8 weeks after parathyroidectomy. Initial post-operative PTH was low at 14.3 pg/mL with calcium remaining elevated at 10.7 mg/dL. One month after surgery, calcium was in normal range at 9.8 mg/dL and PTH had also normalized to 58.5 pg/mL. She experienced no hypocalcemia symptoms or vertebral fractures since her surgery or follow up denosumab injections. Presentation: Monday, July 14, 2025