Background: (131)I 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 (131)I to be administered inversely depends on thyroid radioactive iodine uptake (RAIU). In patients with low RAIU, we evaluated the efficacy of (131)I 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 enrollment, 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 (131)I was aimed to give the thyroid a dose of 100 Gy, by the formula: (131)I activity = 370 MBq × TV (mL)/RAIU(%), taking into account RAIU value after rhTSH for LUG patients. Patients were re-evaluated 3 and 12 months after therapy.
Results: At enrollment, 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 (131)I 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 (131)I activity without loss of effectiveness. In patients with low RAIU, rhTSH pre-treatment may optimize (131)I therapy.