Radioiodine 131I Treatment for Large Nodular Goiter: Recombinant Human Thyrotropin Allows the Reduction of Radioiodine 131I Activity to Be Administered in Patients with Low Uptake

Background: I-131 therapy is effective in reducing the volume of large nodular goiters (thyroid volume [TV]), mainly after stimulation with recombinant human thyrotropin (rhTSH). The amount of I-131 to be administered inversely depends on thyroid radioactive iodine uptake (RAIU). In patients with low RAIU, we evaluated the efficacy of I-131 treatment at lower doses with respect to those calculated on the basal RAIU, after rhTSH stimulation. Methods: Eighteen consecutive patients (17 women and 1 man, 49-83 years) with large nodular goiter were included in the study. At enrolment, 24th h RAIU, TSH, free thyroxine, free triiodothyronine, thyroglobulin antibodies, thyroid peroxidase antibodies, TSH receptors antibodies, urinary iodine, and TV were measured. RAIU was < 40% in 11 patients (lower uptake group [LUG]) and > 40% in 7 (higher uptake group [HUG]). RAIU difference in the two groups was significant (p < 0.0001). LUG patients were treated with rhTSH (0.03 mg i.m.) and RAIU was measured again after 24 hours. The administered amount of I-131 was aimed to give the thyroid a dose of 100 Gy, by the formula: I-131 activity 370MBqxTV (mL)/RAIU(%), taking into account RAIU value after rhTSH for LUG patients. Patients were re-evaluated 3 and 12 months after therapy. Results: At enrolment, LUG and HUG patients did not differ for TV, free thyroxine, free triiodothyronine, TSH, and urinary iodine. LUG patients were older than HUG patients (p = 0.027). In LUG, the uptake increased after rhTSH (42.8% [36%-47.5%] vs. 30% [23.4%-31.6%], p = 0.0044). The I-131 activity was 1073 MBq (740-1103 MBq) in LUG and 851 MBq (677-918 MBq) in HUG (p = 0.22, NS), vs. 1300 MBq (1077-2150 MBq) in LUG, based on RAIU before rhTSH. At 3 and 12 months after radioiodine, TV was reduced to 74% [59%-84%] and 53% [42%-72%] in LUG and 75% [70%-77%] and 65% [54%-74%] in HUG, respectively. The reduction was significant with respect to the basal, both at 3 and 12 months, but not different between the two groups. Conclusions: One single dose of 0.03 mg of rhTSH increased the thyroid RAIU by 40% in patients with nodular goiter and low basal uptake. This allowed a mean reduction of 36% (26%-42%) in the administered I-131 activity without loss of effectiveness. In patients with low RAIU, rhTSH pre-treatment may optimize I-131 therapy.