Significance of radioiodine uptake at 72 hours versus 24 hours after pretreatment with recombinant human thyrotropin for enhancement of radioiodine therapy in patients with symptomatic nontoxic or toxic multinodular goiter.

Objective: To report the effects of pretreatment with recombinant human thyrotropin (rhTSH) on radioiodine uptake (RAIU) and subsequent radioiodine therapy in 30 patients with symptomatic nontoxic or toxic multinodular goiter.
Methods: Patients received a single injection of rhTSH (0.1 mg in 21 and 0.3 mg in 9 patients). Thyroid function tests were performed before and 72 hours after rhTSH administration. Both 4-hour and 24-hour RAIU studies were done after rhTSH administration and repeated at 48 to 52 hours and at 72 hours, respectively. Then all patients were treated with 30 mCi of 131 I.
Results: All study patients experienced symptomatic relief by 1 to 2 months. In addition to the previously reported twofold increase over the baseline RAIU at 24 hours, we found that a second 24-hour RAIU showed a further twofold increase (quadrupling of the RAIU over baseline) at 72 hours after administration of 0.1 mg of rhTSH (from 22% to 43%; P<0.001) and 0.3 mg of rhTSH (from 16% to 37%; P = 0.002), with no significant difference between doses on the RAIU at 24 hours or at 72 hours. Additionally, the RAIU value at 4 hours and 52 hours after administration of 0.1 mg and 0.3 mg of rhTSH revealed a fourfold increase for each dose--from 7% to 28% (P<0.001) and from 5% to 21% (P = 0.002), respectively.
Conclusion: In patients with symptomatic toxic or nontoxic multinodular goiter, 0.1 mg and 0.3 mg of rhTSH were equally efficacious at inducing a quadrupling of the low or low-normal baseline RAIU values at 72 hours after injection. Subsequent radioiodine therapy alleviated compressive and thyrotoxic symptoms in all 30 treated patients. Future studies should help determine doses of rhTSH and radioiodine therapy that are optimal in iodine-sufficient and insufficient regions of the world.