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Endocrine Abstracts (2016) 41 GP207 | DOI: 10.1530/endoabs.41.GP207

1Department of Endocrinology, Diabetes and Metabolism, Centro Hospitalar e Universitário de Coimbra, Coimbra, Portugal; 2Department of Nuclear Medicine, Centro Hospitalar e Universitário de Coimbra, Coimbra, Portugal; 3Faculty of Medicine, University of Coimbra, Coimbra, Portugal.


Introduction: Radioiodine (131I, RAI) is a safe and effective option for the treatment of Graves’ disease (GD). However, approximately 20% of RAI treated patients will have persistent disease or will relapse after the first treatment. Our aim was to identify the factors influencing the outcomes in RAI treatment for GD.

Methods: We analysed 143 DG patients (116 women) treated with RAI between October 2002 and April 2014 and ≥12 months of follow-up. Patients were assessed before (thyroid ultrasonography, thyroid scintigraphy, thyroid-stimulating hormone, free T4, free T3, and thyrotropin receptor antibodies (TRAbs)) RAI, and after 3, 6 and 12 months (thyroid-stimulating hormone, free T4) after RAI. Patients stopped antithyroid drugs 7 days before RAI. Successful treatment was defined as euthyroidism or hypothyroidism, 12 months after RAI treatment and no need for antithyroid drugs or additional RAI treatments.

Results: Therapeutic success was achieved in 80.4% of DG patients. Hypothyroidism prevalence increased during the study course; 43.2, 72.4, and 87% of patients had hypothyroidism at 3, 6, and 12 months, respectively. Univariate analysis showed TRAbs, functioning thyroid mass, and administered activity of RAI were significantly higher in patients with unsuccessful RAI treatment (48.2 U/l vs 20.0 U/l; 77.8 g vs 48.1 g; 517 vs 398 MBq, respectively). However, multiple logistic regression analyses demonstrated that only functioning thyroid mass was inversely associated with RAI success (odds ratio [OR]=0.89, CI=0.83–0.96, P=0.004), particularly for estimated thyroid masses ≥60 g (sensitivity=78%, specificity=82%, likelihood ratio=4.4, P<0.001).

Previous treatment with methimazole, absence of thyroid nodules (≥1 cm), and scintigraphic homogeneous radiotracer uptake were associated with hypothyroidism development. Multivariate logistic regression confirmed previous treatment with methimazole and higher risk for hypothyroidism development (OR=10.3, CI=0.02–0.56, P=0.009).

Conclusion: RAI was successful in most (80%) patients. Higher thyroid masses were associated with lower success rates. Patients previously treated with methimazole have higher probability of developing hypothyroidism after RAI treatment.

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