The aim of the study was to assess whether stimulation by
recombinant human TSH (
rhTSH) may be used in patients with differentiated
thyroid carcinoma for postsurgical ablation of thyroid remnants using a 30-mCi standard dose of (131)I during
thyroid hormone therapy. The rate of ablation was prospectively compared in three groups of patients consecutively assigned to one of three treatment arms: in the first arm, patients (n = 50) were treated while hypothyroid (HYPO); in the second arm, patients (n = 42) were treated while HYPO and stimulated in addition with
rhTSH (HYPO +
rhTSH); in the third arm, patients (n = 70) were treated while euthyroid (EU) on
thyroid hormone therapy and stimulated with
rhTSH (EU +
rhTSH). The outcome of thyroid ablation was assessed by conventional HYPO (131)I scan performed in HYPO state 6-10 months after ablation. Basal serum TSH was elevated in the HYPO and HYPO +
rhTSH groups. In the EU +
rhTSH group, basal serum TSH was 1.3 +/- 2.5 micro U/ml (range, <0.005-11.9 micro U/ml). After
rhTSH, serum TSH significantly increased in the HYPO +
rhTSH group and the EU +
rhTSH group. Basal 24-h radioiodine thyroid bed uptake was 5.8 +/- 5.7% (range, 0.2-21%) and 5.4 +/- 5.7% (range, 0.2-26%) in the HYPO and HYPO +
rhTSH groups, respectively. In the HYPO +
rhTSH group, mean 24-h thyroid bed uptake rose to 9.4 +/- 9.5% (range, 0.2-46%) after
rhTSH (P < 0.0001). The 24-h uptake after
rhTSH in the EU +
rhTSH group was 2.5 +/- 4.3% (range, 0.1-32%), significantly lower (P < 0.0001) than that found in the HYPO and HYPO +
rhTSH groups. The rate of successful ablation was similar in the HYPO and HYPO +
rhTSH groups (84% and 78.5%, respectively). A significantly lower rate of ablation (54%) was achieved in the EU +
rhTSH group. Mean initial dose rate (the radiation dose delivered during the first hour
after treatment) was significantly lower in the EU +
rhTSH group (10.7 +/- 12.6 Gy/h) compared with the HYPO +
rhTSH group (48.5 +/- 43 Gy/h) and the HYPO group (27.1 +/- 42.5 Gy/h). In conclusion, our study indicates that by using stimulation with
rhTSH, a 30-mCi standard dose of radioiodine is not sufficient for a satisfactory thyroid ablation rate. Possible reasons for this failure may be the low 24-h radioiodine uptake, the low initial dose rate delivered to the residues, and the accelerated
iodine clearance observed in EU patients. Possible alternatives for obtaining a satisfactory rate of thyroid ablation with
rhTSH may consist of increasing the dose of radioiodine or using different protocols of
rhTSH administration producing more prolonged thyroid cells stimulation.