Sustained and diffuse 131I avid bone metastases with low thyroglobulin levels in a patient with papillary thyroid carcinoma.

A 63-year-old man with papillary thyroid carcinoma (PTC) and bone metastases was treated with 131I residual thyroid ablation (RTA) and 2 repeated post-ablation 131I therapies after total thyroidectomy. 131I whole-body scans (WBS) demonstrated sustained and diffuse 131I avid bone metastases, accompanied by persistent very low thyroglobulin (Tg) levels and negative antithyroglobulin antibody (TgAb) in post-ablation 131I therapies in hypothyroid state after levothyroxine withdrawal. The spread of bone metastases were found on the last therapeutical 131I WBS. The benefit of 131I therapy after levothyroxine withdrawal should be weighed even if the metastases are 131I avid in poorly differentiated thyroid carcinoma.