Remarkable Response of Pulmonary Metastases Rather Than Remnant Thyroid in 131I Therapy of Follicular Thyroid Cancer.

A 66-year-old man with follicular thyroid cancer after total thyroidectomy was referred for I therapy. Thyroid function tests before I administration exhibited severe thyrotoxicosis although the patient did not take levothyroxine after thyroidectomy. A 185 MBq I whole-body scintigraphy and SPECT/CT revealed multiple iodine-avid pulmonary metastases with the largest tumor diameter of 1.4 cm and remnant thyroid. A diagnosis of thyrotoxicosis caused by hyperfunctioning pulmonary metastases was then made. The patient was administered 7.4 GBq of I. Six months after I therapy, a significant reduction of the pulmonary metastatic disease and thyroglobulin level was observed. However, the remnant thyroid was still visualized.