Functioning metastases from differentiated thyroid carcinoma are rare and present a great therapeutic challenge. Here, we present an unusual case of a patient with metastatic thyroid carcinoma who developed a hyperthyroid state a few years after the diagnosis due to functioning metastases. Radioiodine treatment was effective in controlling the hyperthyroidism; however, it had no effect on tumor burden. By sharing our experience with this case, we hope to raise awareness for this rare condition and the ways to manage it.
