Discrepancy of Diagnostic and Post-Therapeutic Radioiodine Whole Body Scans in a Follicular Thyroid Carcinoma Patient with Multiple Bony Metastases

Received 3/28/2004; revised 5/3/2004; accepted 5/8/2004. For correspondence and reprints contact: Cheng-Yi Cheng, M.D., Department of Nuclear Medicine, Tri-Service General Hospital, 325 Section 2, Cheng-Kung Road, Neihu, Taipei 114, Taiwan. Tel: (886)2-87927374, Fax: (886)2-87927217, E-mail: [email protected] A large amount of radioiodine-131 (I) is the main choice for treatment of follicular thyroid carcinoma with multiple bony metastases. However, the curative rate is not encouraging. A 40-year-old woman who had received a thyroidectomy due to follicular thyroid cancer was referred to our department for the I cancer workup. She did not have bone pain or other clinical manifestations regarding bony metastases. Serum thyroglobulin (Tg) value in thyroxine withdrawal was 29.9 ng/mL. The diagnostic I whole body scan (WBS, 2 mCi) showed multiple bony metastases. A 200 mCi of I was thus given. Interestingly, the image pattern of the post-therapeutic WBS was quite different from that seen on the diagnostic scan, which showed a large decrease in numbers of bony metastases. Therapeutic and/or stunning effects of the diagnostic I might contribute to the discrepancy. Negative I WBS with stimulated serum Tg values less than 2 ng/mL, however, were found at 6 months and at 2 years after therapy.