Detection of Functioning Thyroid Cancer Metastasis on Whole Body Pertechnetate Scintigraphy.

Thyrotoxicosis due to functioning metastases in differentiated thyroid cancer (DTC) is exceedingly rare. It may constitute confusing diagnostic as well as present therapeutic challenges. We present here two patients, a discussion and literature review on the subject. The patients presented initially with thyrotoxicosis and on routine 99mTc pertechnetate thyroid scan extrathyroidal foci of uptake were found, subsequently leading to the diagnosis of metastatic thyroid cancer. Histology showed both cases as follicular thyroid carcinoma. In one patient 18F-FDG displayed the metastases despite these foci exhibiting iodine avidity at an earlier 131-1 diagnostic scan. Both patients later received radioiodine in therapy doses. One patient had a pre-therapy total thyroidectomy. The other did not because of a relapse of his thyrotoxicosis even though he had been vigorously treated with anti-thyroid drugs. He received 131-1 therapy as palliation. Both patients are doing well on thyroxine replacement in suppressive doses and are being followed up. TC-99m pertechnetate whole body scan is showed here as useful in the detection of functioning distant metastases from differentiated thyroid carcinoma although 131-1 Whole Body Scan (WBS) is still generally considered the method of choice.