Clinical experience with recombinant human thyroid-stimulating hormone (rhTSH): whole-body scanning with iodine-131

Whole-body scanning (WBS) with iodine-131 (I-131) is currently used together with serum thyroglobulin (Tg) measurement in the diagnostic follow-up of well-differentiated thyroid carcinoma. One of the main disadvantages of I-131 WBS is its requirement of repeated weeks-long withdrawal of thyroid hormone suppression therapy (THST) to raise endogenous thyroid-stimulating hormone (TSH) production. This results in hypothyroidism and associated abnormalities, discomfort and morbidity. Recently, however, a series of multicentre clinical studies established the efficacy, safety, non-antigenicity, and quality of life benefits of recombinant human TSH (rhTSH, Thyrogen, thyrotropin alfa, Genzyme Corporation, Cambridge, MA, USA) in promoting radioiodine uptake and permitting sensitive I-131 WBS in patients on THST after initial therapy of well-differentiated thyroid cancer. Thus in everyday practice, rhTSH administration may in many cases supersede THST withdrawal as a preparative method for I-131 imaging. With the use of rhTSH, as whenever I-131 WBS is performed, useful and accurate imaging requires meticulous attention to good scanning practices. These include use of appropriate equipment, proper timing, sufficient scanning time, vigilance against artifacts and iodine contamination, and consideration of additional imaging in the case of ambiguous 48-hour scans. Whole-body retention of I-131 is approximately 50% greater during hypothyroidism after THST withdrawal than during euthyroidism on THST and rhTSH. Therefore, it is important to use an adequate diagnostic activity of > or =4 mCi (148 MBq) to compensate for the faster radioiodine clearance in the euthyroid state permitted by rhTSH administration. Ongoing dosimetric research eventually may provide more specific guidance regarding radioiodine activities for diagnostic, and, particularly, therapeutic purposes, with the use of rhTSH.