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Usefulness of the Determination of the Early Radioiodine Thyroid Uptake Test in Prediction of Outcome of Graves-Basedow Hyperthyroidism during Antithyroid Drugs Treatment

Introduction: Antithyroid drugs may be proposed as the first line therapy for hyperthyroidism due to Graves-Basedow disease. But, as the response to antithyroid drugs treatment for Graves-Basedow disease is unpredictable, it would be useful to have test that could predict outcome during treatment and, therefore, to initiate the most appropriate form of therapy in individual patients. Aim: To evaluate the usefulness of the determination of the early radioiodine thyroid uptake test in predicting both persisting hyperthyroidism and the onset of remission during antithyroid drugs therapy of hyperthyroidism. Patients and Methods: We performed a retrospective survey of 67 patients (58 women and 9 men ; mean age 36 years), from our thyroid clinic database, presenting with a first episode of Graves-Basedow disease. Graves-Basedow disease was defined as the presence of biochemical hyperthyroidism (raised serum free T4 and T3 concentration and undetectable TSH) together with the diffuse goiter and significant titer of thyroid peroxidase and/or thyroglobulin autoantibodies. Our policy over the period of the study was to offer a course of an antithyroid drug (carbimazole or propylthiouracil) combined with L-thyroxine for 12 - 18 months in the hope of achieving remission. Early thyroid uptake test (TST) was performed 10 minutes after intravenously injected 370 KBq (10 µCi) Iodine-131. TST was estimated every 6-8 weeks together with thyroid hormone during combined therapy with antithyroid drugs and L-thyroxine. Remission was defined when TST reached value below 4% together with suppressed TSH and normalized FT4 and FT3. Results: By using a cut-off limit of 4% TST outcome of Graves’ hyperthyroidism after a course of antithyroid drugs was 1) successful (euthyroid for at least 6 months after withdrawal of thionamide treatment) in 50 patients, and 2) failed (persistent or relapsed disease after a full course of thionamide treatment) in 17 patients. In 7 of them radioiodine therapy was considered, in 4 younger patients surgery was advised and in 6 patients antithyroid drugs treatment was continued. Conclusion: Determination of the early radioiodine thyroid uptake test can be a useful guide to management of Graves-Basedow hyperthyrodism by promptly identifying patients likely to benefit from antithyroid drugs treatment from those with permanent hyperthyroidism who need further radical (radioiodine or surgery) therapy.

Treatment Outcome; hyperthyroidism; Thyroid function test

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