Intrathyroidally located parathyroid carcinoma is extremely rare cause of primary hyperparathyroidism. Multifocal papillary and follicular thyroid carcinomas are rather common.
We report a case of 40-year old man presenting with substantial weight loss, anemia and multiple osteolytic lesions of both tibias. Peak serum calcium level was 5.0 mmol/l, parathyroid hormone (PTH) level was 989 pg/ml. Left thyroid lobe was firm and enlarged. Routine percutaneous fine needle aspiration (FNA) of intrathyroidal mass disclosed poorly differentiated follicular thyroid carcinoma. FNA of the nodule beneath the left lobe indicated parathyroid origin, possibly parathyroid neoplasm. We performed en block resection of the left thyroid lobe and the nodule beneath it. Frozen section identified likely medullary carcinoma, as well proven in mediastinal lymph node which was previously misinterpreted as enlarged parathyroid gland. Total thyroidectomy and bilateral modified radical neck dissection were then performed. Negative thyroglobulin and calcitonin, but positive PTH expression confirmed parathyroid carcinoma with a single upper mediastinal lymph node metastasis and multiple diffuse microscopic metastases in both thyroid lobes.
This is the first reported case of parathyroid carcinoma with multiple foci within thyroid tissue. Presurgical and intraoperative diagnosis of parathyroid carcinoma can be difficult, especially if located within thyroid gland. In patients with primary hyperparathyroidism and intrathyroid suspicion of malignancy finding, parathyroid carcinoma should be considered. The exact mechanism of intraglandular multifocal thyroid carcinomas has not been determined yet. The first reported presence of multiple foci of intrathyroid parathyroid carcinoma, suggests the intraglandular dissemination of the primary tumor is the main mechanism of multifocality.