MON-840 - Persistent Normocalcemic Hyperparathyroidism after Autotransplantation of Parathyroid Gland

Background:
Parathyroid autotransplantation of the forearm is associated with possible complications. In this case, we discuss an unusual presentation of severe hyperparathyroidism without hypercalcemia.

Case:
A 48-year-old female with papillary thyroid carcinoma (PTC) post total thyroidectomy and radioactive iodine was diagnosed with primary hyperparathyroidism eight years later. She was initially found to have a calcium of 11.5 mg/dL (8.5-10.3 mg/dL) and an elevated PTH of 182 pg/mL (15-65 pg/mL). Technetium-99m sestamibi scan revealed an 11 mm anterior mediastinal parathyroid adenoma. Given the degree of hypercalcemia, she underwent parathyroidectomy with autotransplantation of a partial parathyroid gland to the left forearm due to low PTH intraoperatively. Three years later, the patient was noted to have a PTH of 735 pg/mL, calcium of 9.3 mg/dL, and 25-vitamin D level of 36 ng/mL (30-100 ng/mL). CT neck did not show suspicious enhancement to suggest recurrent disease. Thyroglobulin levels remained low, with no suspicion of progression of PTC. US of the left forearm evaluated the autotransplant, which showed a 0.3 cm subcutaneous mass. Repeat labs showed a PTH of 961 pg/mL and calcium of 8.8 mg/dL. The patient continued to be asymptomatic without hypercalcemia or other manifestations, including normal DXA. Due to the discrepancy between lack of clinical symptoms and biochemical findings, a repeat lab draw on the contralateral arm resulted in a normal PTH of 64 pg/dL and calcium of 8.9 mg/dL. Further evaluation was deferred with consideration of repeat imaging or resection if the patient develops clinical hypercalcemia.

Discussion:
This is an uncommon presentation of non-clinically relevant hyperparathyroidism after parathyroidectomy with autotransplantation. Several case reports have documented hyperparathyroidism after an autotransplanted graft underwent autonomous hyperfunctioning, hyperplasia, or infiltrative growth, as the gland transplanted can often be abnormal in pathology. We suspect that the patient had an infiltrative growth of the parathyroid gland that was not captured on US, resulting in higher-than-expected PTH levels when labs were drawn on the transplanted side. Other studies also suggest using thallium/technetium scanning to evaluate supernumerary or distant ectopic glands; however, the decision was deferred as the patient did not have hypercalcemia.

Conclusion:
In patients who undergo parathyroid autotransplantation after removal of a parathyroid adenoma, it is important to consider long-term manifestations, including hyperplasia, infiltrative growth, or ectopic gland, and different strategies for evaluation, including imaging or other laboratory evaluation.

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