Carcinoma of the thyroid manifested as hyperthyroidism caused by functional bone metastasis.

A rare case of hyperthyroidism in the presence of a functioning bone metastasis secondary to an occult thyroid cancer is reported. A 59-year-old woman's pelvic bone metastasis was much too extensive and hypervascular to permit resection. An I-131 scan showed striking activity in the pelvic metastasis, which reflected ectopic excessive production of thyroid hormone by a functioning metastatic thyroid carcinoma. After total thyroidectomy, the patient received I-131 ablation and transcutaneous intra-arterial embolization therapy but her metastasis progressively enlarged. Microscopically, concomitant follicular and papillary cancer was found in close proximity to the thyroid. The patient now has vertebral metastases, and her hyperthyroid state still requires methymazole to prevent thyrotoxicosis.