Partial Stunning in Thyroid Remnant After Administration of Scanning Dose Followed By 100 mCi I-131 Therapy

A 24-year-old woman with papillary thyroid carcinoma was imaged with 5 mCi of I-131, 2 months after thyroid surgery. Preablation imaging demonstrated focal uptake in six different areas in the thyroid remnant. After administration of 100 mCi of an ablation dose, repeat imaging was performed on the fifth day when the patient's residual activity fell below 30 mCi. Only two focal radioiodine uptake areas were observed in the neck region, whereas four of six other focuses in the preablation scan showed no uptake. Although the exact explanation of the partial suppression of the thyroid remnant, as in this interesting case, is not known, it may be due to an elevated radioiodine uptake and suppression by the 5 mCi scanning dose of I-131 on the areas without uptake. The authors conclude that future investigations on this findings are necessary.