A Rare Cause of Thyrotoxicosis: Metastasis of Ovarian Clear Cell Carcinoma to the Thyroid Gland.

Metastases to the thyroid gland are rare, accounting for up to 2% of all thyroid malignancies. Ovarian cancer metastasizing to the thyroid is exceedingly uncommon, with only a few cases reported in the literature. We present the case of a 36-year-old female individual with a history of metastatic ovarian clear cell carcinoma and known thyroid metastasis who presented with shortness of breath, dysphagia, and palpitations. Laboratory evaluation revealed undetectable thyroid-stimulating hormone (TSH), elevated free thyroxine (fT4) and triiodothyronine (fT3), and markedly increased serum thyroglobulin levels. A computed tomography (CT) scan of the neck demonstrated diffuse thyroid infiltration with compressive features. The patient was diagnosed with thyrotoxicosis and treated with methimazole, prednisone, and metoprolol. To our knowledge, this is the first reported case of ovarian clear cell carcinoma with thyroid gland metastasis presenting with concomitant thyrotoxicosis. Although thyroid metastases are rare and typically nonfunctional, they should be considered in patients with known malignancy who develop new thyroid dysfunction, particularly when biochemical or imaging findings are atypical for thyroiditis or autoimmune thyroid disease. Recognizing this entity is important, as timely distinction from more common causes of thyrotoxicosis can guide appropriate, patient-centered management.