PGY-3 NYMC/Metropolitan Hospital New York, New York, United States
Introduction : Bisphosphonates are a popular choice in treating bone metastasis as they inhibit osteoclastic action and are readily available. However, in cases of skeletal metastasis secondary to thyroid cancer requiring total thyroidectomy, bisphosphonates should be preferably avoided. It can cause overt hypocalcemia due to probable parathyroid damage from total thyroidectomy, as in the case presented. Instead, observation should be considered in stable patients and radiotherapy in others.
Case(s) Description : A 73-year-old female with a history of refractory papillary thyroid cancer managed with total thyroidectomy, laryngectomy, and RAI ablation on Lenvatinib for five years was found to have an enhancing lesion on the left thyroid bed. The biopsy was unsatisfactory. The Thryoglubin levels were trending up from 196 to 741 ng/mL. A whole body scan I- 131 showed increased uptake in a lesion over the lumbar spine diagnosed as bone metastasis, and thus, the patient was started on zoledronic acid. After one dose of zoledronic acid, the serum calcium dropped to 5.3 mEq/L. The patient was immediately recalled to the oncology clinic and received appropriate supplementation. Since the patient has undergone total thyroidectomy, she also likely had a parathyroid injury or stunted parathyroid with ineffective calcium regulation.
Discussion : Management of skeletal metastasis can be challenging in patients who have undergone total thyroidectomy. About 12% of such patients have had iatrogenic resection or injury of parathyroid glands, placing them at risk for hypocalcemia. Some articles suggest supplementing calcium and vitamin D in all patients post-total thyroidectomy. Bone metastases happen in 4% of all thyroid cancers and are thought to be osteoclast-mediated. Some experts recommend bisphosphonate use in the management of bone metastasis, but no guidelines contradict its use in patients with post-total thyroidectomy. Due to its easy availability, it might be prematurely prescribed if the possibility of stunted or resected parathyroid glands is not considered, which is what happened in the case mentioned above.
