Purpose: Reports state that scan results for as many as 25% of patients with differentiated thyroid carcinoma will convert to iodine-131 (I-131) negative over time with positive thyroglobulin levels. Tl-201, positron emission tomography (PET), and sestamibi or tetrofosmin have all helped to identify I-131-negative thyroid carcinomas. The authors have identified a case of reversal of I-131 findings from negative to positive after short-term thyroxine withdrawal combined with treatment with recombinant human thyroid-stimulating hormone (rhTSH).
Materials and methods: The authors obtained multiple I-131 whole-body scans with 4-week thyroid hormone withdrawal, post-I-131 therapy scans, nonthyroid withdrawal Tl-201 chloride whole-body tumor images, and finally combined 2.5-week thyroid hormone withdrawal and rhTSH-stimulation I-131 whole-body scans before and after therapy.
Results: The authors examined one patient during a period of 9 years whose I-131 whole-body scan results were at first positive and then became negative. After a combination of rhTSH stimulation and thyroid hormone withdrawal, the results changed again to I-131 positive.
Conclusions: This is the first known case in which I-131 findings changed from negative to positive. A combination of rhTSH stimulation and nearly adequate withdrawal may help convert more I-131-negative whole-body scans to positive.