Recurrent hyperparathyroidism due to proliferation of autotransplanted parathyroid tissue in a multiple endocrine neoplasia type 2A patient

About 20%–30% of all cases of multiple endocrine neoplasia type 2A (MEN 2A) is accompanied by primary hyperparathyroidism. These patients undergo parathyroidectomy and, if needed, autotransplantation. In rare cases, autotransplanted parathyroid tissues can cause hypoparathyroidism due to failure of transplantation or hyperparathyroidism due to proliferation of the transplanted tissue. A 68-year-old female with MEN 2A underwent left adrenalectomy for pheochromocytoma 15 years prior to presentation and total thyroidectomy, central and right lateral neck lymph node dissection, and subtotal parathyroidectomy with autotransplantation for medullary thyroid cancer and primary hyperparathyroidism 6 years previous. Recently, a doubtful parathyroid adenoma was detected in the left sternocleidomastoid muscle on ultrasonography and on an additional sestamibi scan. The mass was excised and histologically confirmed as parathyroid adenoma. This is a very rare case, and it suggests that long-term regular monitoring of serum calcium and intact parathyroid hormone levels is necessary after parathyroid autotransplantation.