Recombinant human thyroid-stimulating hormone is effective for radioiodine ablation of post-surgical thyroid remnants

Objective To investigate whether recombinant human thyroid-stimulating factor (rhTSH) is effective for the radiometabolic ablation of post-surgery thyroid remnants, using low doses of I-131. Patients and methods The study included two groups of patients enrolled consecutively: group 1 consisted of 52 patients with papillary cancer or minimally invasive follicular cancer (stage I and 11), and group 2 consisted of 41 patients with the same stage of disease. All patients underwent a total thyroidectomy. Group 1 received 1.11 GBq (30 mCi) I-131 for post-surgical remnants ablation with the aid of rhTSH, while group 2, in the hypothyroid state, received the same amount of radioiodine. To minimize iodine interference, all patients remained on a low iodine diet for 2 weeks and L-thyroxine (L-T4) was stopped for 4 days in the group of patients treated with the aid of rhTSH. To investigate I-131 uptake in this group, a tracer dose was administered 3 h after the second injection of rhTSH and the uptake was evaluated at 24 h just before administration of the therapeutic dose. I-131 was also measured in the patients treated in the hypothyroid state just before the therapeutic dose was given. Results After 1 year both groups were studied by using whole-body scintigraphy (WBS) and measuring thyroglobulin after rhTSH. In group 1, WBS was negative in 76.9% (40 patients), while thyroglobulin-stimulated levels were < 1.0 ng(.)ml(-1) in 86.5% (45 patients). In Group 2, WBS was negative in 75.6% (31 patients), while thyroglobulin-stimulated levels were < 1 ng(.)ml(-1) in 78.0% (32 patients). I-131 uptake was 2.29 +/- 0.45 in the group treated with the aid of rhTSH, and 3.30 +/- 0.7 in the group treated in the hypothyroid state (P=0.2). No patients treated with the aid of rhTSH and with the short stoppage of L-T4 experienced symptoms of hypothyroidism, and free thyroxine (FT4) and thyroid-stimulating hormone levels remained normal. Conclusions Our data confirm that, when the interference of iodine is minimized, rhTSH is highly effective for the treatment of post-surgical thyroid remnants using a low dose of I-131.