Recombinant human thyrotropin markedly changes the I-131 kinetics during I-131 therapy of patients with nodular goiter: An evaluation by a randomized double-blinded trial

The present study compares, in a randomized double-blinded design, the expected and the actual absorbed thyroid radioactive dose in response to 0.3 mg recombinant human (rh)TSH (n = 35) or placebo (n = 28) given 24 h before I-131 therapy in patients with nodular goiter (median volume, 69 ml; range, 20-440 ml). The I-131 activity calculation was based on thyroid I-131 uptake (RAIU) at 24 and 96 h after a tracer dose of 0.5 MBq I-131. After I-131 therapy, 24- and 96-h RAIU were repeated allowing a more exact assessment of the actual absorbed thyroid dose. The median I-131 activity was 617 and 632 MBq, respectively, in the rhTSH and the placebo group. At baseline, the 24- and 96-h RAIU and the expected thyroid dose were 32.8 +/- 9.1%, 32.1 +/- 8.2%, and 96.3 +/- 16.3 Gy, respectively, in the rhTSH group and 35.7 +/- 11.8%, 35.2 +/- 11.3%, and 94.1 +/- 18.5 Gy, respectively, in the placebo group (P value not significant between groups). After I-131 therapy, the 24- and 96-h RAIU and the actual absorbed thyroid dose were 46.9 +/- 11.7%, 45.0 +/- 12.1%, and 136.7 +/- 47.9 Gy, respectively, in the rhTSH group and 33.0 +/- 11.4%, 31.0 +/- 11.3%, and 76.9 +/- 27.5 Gy, respectively, in the placebo group (P < 0.001 between groups). Comparing the expected with the actual absorbed thyroid dose, this corresponds to a mean increase of 36.4% (95% confidence interval, 21.3-53.4) in the rhTSH group and a decrease of 21.5% (95% confidence interval, -33.9 to -6.6) in the placebo group (P < 0.001), equivalent to an increase of 73.8% in the absorbed thyroid dose in the rhTSH-treated group. We have thus for the first time shown that stimulation with rhTSH before I-131 therapy not only hinders the decrease in the thyroid RAIU observed with conventional I-131 therapy but in fact also significantly enhances the absorbed thyroid dose. Whether this also leads to a significant increase in goiter size reduction needs additional study.