Intrathyroidal parathyroid carcinoma as cause of hypercalcemia and pitfall of localization techniques: clinical and biologic features.

OBJECTIVE

To describe an unusual case of intrathyroidal parathyroid carcinoma (PC), which was retrospectively diagnosed in a woman who underwent surgical treatment of a recurrent nodular goiter.

METHODS

We report the clinical and biologic features of an intrathyroidal PC, discuss the challenges with distinguishing PC from parathyroid adenoma, and review the related literature.

RESULTS

A 67-year-old woman sought medical attention for dysphagia attributable to the recurrence of a normal functioning multinodular goiter. Thyroid ultrasonography disclosed a 3-cm solid inferior nodule. Because she refused surgical treatment and a trial of levothyroxine was unsuccessful, periodic follow-up examinations were scheduled. At 1-year follow-up, hypercalcemia (12.1 to 12.6 mg/dL) and low phosphorus levels (2.0 to 2.3 mg/dL) were found, and parathyroid hormone (PTH) levels were profoundly increased (481 to 721 pg/mL). Neck ultrasonography showed a large hypoechogenic solid nodule, not clearly cleaved from the right thyroid lobe, which was possibly compatible with an enlarged parathyroid gland; however, a sestamibi scan was negative. During total thyroidectomy, intraoperative frozen sections of the intrathyroid nodule were compatible with nodular goiter with cellular pleomorphism. Final histologic examination showed cellular nests with nuclear pleomorphism and invasive behavior into the thyroid tissue and likely into the vessels, in conjunction with immunohistochemical negativity for thyroglobulin and strong positivity for PTH. These findings were highly suggestive of and supported the diagnosis of PC. Postoperatively, calcium levels normalized, and PTH values declined considerably but remained slightly increased. Vitamin D supplementation helped normalize the PTH levels. The patient has undergone follow-up for 5 years and has shown no morphologic or biochemical signs of tumor recurrence.

CONCLUSION

PC is a rare entity but should be suspected in patients with hypercalcemia, substantially increased PTH levels, and a neck mass. In such patients, techniques such as sestamibi scanning may fail to localize the neoplasm. Surgical treatment remains the preferred technique for an optimal outcome of the disease. Nevertheless, lifelong follow-up is necessary.