Endocrine Abstracts

Background: Graves’ disease (GD) is an autoimmune disorder of thyroid gland and is the first cause of hyperthyroidism. Radioactive iodine (RAI) therapy is the most used second- line treatment after failure of anti-thyroid drugs. The optimal RAI’s activity to be administered may be predetermined or calculated. Whether the latter is better is still a matter of debate.

Aim: To compare the risk of persistent hyperthyroidism in GD patients treated with predetermined vs calculated dose of RAI.

Materials and Methods: Retrospective analysis of 176 patients affected by GD (F: 126, M: 50), divided in: Group A, consisted of 141 patients treated by predetermined (10 or 15 mCi) RAI activity and Group B, consisted of 35 patients treated by calculated dose of RAI (Traino’s formula). Uni- and multivariate logistic regression analysis was used to estimate factors associated with persistent hyperthyroidism after 40 days, 3 and 6 months from the RAI therapy.

Results: The baseline features of the two groups were not different except for the pretreatment thyroid volume (23.1 vs 16.6 ml in Group A and B, respectively; P = 0.002) and TRAb positivity (62.5% vs 85.3% in Group A and B, respectively; P = 0.001). At the multivariate analysis we found that no different risk of persistent hyperthyroidism was observed between predetermined and calculated RAI activity at 40 days (OR= 3.5, 95%CI= 1.0-12.5; P = 0.06), 3 months (OR= 1.3, 95%CI= 0.4-4.0; P = 0.66) and 6 months (OR= 0.55, 95%CI= 0.2-1.8; P = 0.32) after the treatment. At 6 months RAI therapy induced hypothyroidism or euthyroidism in 73.8% of Group A and 68.4% of Group B (P = 0.62) and the only factors independently associated with persistent hyperthyroidism were the pretreatment thyroid volume (5% increasing risk for each ml of increasing thyroid volume) and positivity of TRAb (5-fold increased risk with respect to patients with negative TRAb).

Discussion: According to American and European Thyroid Associations, a single administration of RAI should be administered to achieve hypothyroidism in patients with GD, whereas European Association of Nuclear Medicine considers hypothyroidism a side effect of the treatment. RAI activity calculated through dosimetry method should avoid hypothyroidism and unnecessary ionizing radiation exposure. In this study we found that the risk of persistent hyperthyroidism after 6 months from the RAI therapy was not different between the two methods and the most important parameters influencing the failure of RAI therapy were both pre-therapy thyroid volume and TRAb positivity.

Conclusions: The present study provided no convincing evidence for the superiority between predetermined and dosimetry methods to calculate RAI activity in patients with GD.