PSAT275 A Rare Case of Thyroid-Stimulating Immunoglobulin-Induced Thyrotoxicosis in Poorly Differentiated Metastatic Thyroid Cancer

We report case of a rare of hyperthyroidism secondary to functional metastatic thyroid carcinoma, which is an infrequent phenomenon that can be challenging to diagnose and treat, as low thyroid-stimulating hormone (TSH) levels can suppress the development and growth of differentiated thyroid carcinoma cells. Previous studies have reported that hyperfunctioning thyroid carcinoma may present as autonomous functioning thyroid nodules (AFTN) within the thyroid gland, or as functioning lesions in metastatic foci, which is our case. Functional thyroid carcinomas are capable of absorbing iodine, as well as synthesizing and releasing thyroxine, are often associated with follicular thyroid carcinomas. Potential mechanisms for the thyrotoxicosis include a large aggregate tumor mass, as well as the presence of thyroid-stimulating immunoglobulins (TSIs) that are able to stimulate the thyroid-stimulating hormone (TSH) receptors of the thyroid carcinoma. In this clinical case, patient presented with high titers of TSIs, and metastatic thyroid carcinoma, with persistent hyperthyroidism after thyroidectomy and with a remarkable radioactive iodine treatment response. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.