Recurrent Primary Hyperparathyroidism Due to Adenoma Formation in Autotransplanted Parathyroid Tissue 28 Years After Parathyroidectomy in a Patient With Multiple Endocrine Neoplasia Type 2A.

Primary hyperparathyroidism (PHPT) is an established manifestation of multiple endocrine neoplasia type 2A (MEN2A). In patients requiring extensive parathyroid surgery, autotransplantation of parathyroid tissue may be performed to preserve parathyroid function. Recurrence due to adenoma formation within autotransplanted parathyroid tissue is exceptionally rare. We report a case of a 59-year-old male with genetically confirmed MEN2A caused by a heterozygous RET p.Cys634Tyr (C634Y) mutation who developed recurrent PHPT caused by adenoma formation within autotransplanted parathyroid tissue 28 years after parathyroid surgery with autotransplantation into the sternocleidomastoid muscle. Biochemical evaluation demonstrated hypercalcemia and elevated parathyroid hormone (PTH) levels. Fluorine-18 choline (¹⁸F-choline) positron emission tomography/computed tomography (PET/CT) localized a hyperfunctioning lesion within the autotransplanted parathyroid tissue. Surgical excision resulted in normalization of biochemical parameters, and histopathological examination confirmed a parathyroid adenoma. This case demonstrates that autotransplanted parathyroid tissue may remain capable of adenoma formation decades after transplantation in patients with MEN2A. It underscores the importance of lifelong biochemical surveillance and highlights the value of ¹⁸F-choline PET/CT for accurate localization of recurrent hyperfunctioning autotransplanted parathyroid tissue.