Parathyroidectomy in a patient treated with denosumab: A case report

Primary hyperparathyroidism (PHPT) is most common in postmenopausal women, with parathyroidectomy considered to be the only definitive treatment. The risk of osteoporosis is increased in postmenopausal women and osteoporosis may be a sequela of long-term PHPT. Denosumab, a novel human monoclonal antibody, is a Food and Drug Administration-approved treatment for osteoporosis in postmenopausal women at high risk of fracture. Multiple reports in the literature have observed markedly elevated parathyroid hormone (PTH) after one dose of denosumab. We report our experience of parathyroidectomy in a patient who received a single dose of denosumab two weeks prior to surgery. In that time, the patient's uncorrected calcium level decreased from 10.6 to 8.5 mg/dL and PTH increased from 209 to 465 pg/mL. On ultrasound immediately prior to surgery, a 1 cm hypoechoic focus was identified at the left thyrothymic ligament, suspicious for parathyroid adenoma. A 402 mg mass was removed at this site, with parathyroid tissue confirmed on frozen pathology review. Following removal, intraoperative PTH declined rapidly before plateauing at 200 pg/mL. After discussion of potential denosumab-induced hyperparathyroidism in the setting of multiglandular parathyroid disease, the remaining glands were explored. Removal of two glands on the right yielded a reduction in PTH to 82 pg/mL, with PTH eventually settling at 53 pg/mL postoperatively. Given the difficulty of interpreting intraoperative PTH kinetics in the setting of denosumab-induced hyperparathyroidism, we recommend administration of denosumab be delayed until after parathyroidectomy and that surgeons factor in its effects before deciding to operate on patients who have already received a dose.