Endocrinol Metab.  2022 Jun;37(3):524-532. 10.3803/EnM.2022.1418.

Clinical Outcomes of Repeated Radioactive Iodine Therapy for Graves’ Disease

• Kim MJ
• Cho SW
• Kim YA
• Choi HS
• Park YJ
• Park DJ
• Cho BY

• KMID: 2531396
• DOI: http://doi.org/10.3803/EnM.2022.1418

Abstract

Background
Radioactive iodine (RAI) therapy is a successful therapeutic modality for Graves’ disease. However, RAI therapy can fail, and RAI therapy after antithyroid drugs (ATDs) has a lower remission rate. Therefore, many patients require repeated RAI therapy. This study investigated the clinical outcomes of repeated RAI therapy for Graves’ disease.
Methods
Patients who underwent RAI therapy as second-line therapy after failure of ATD treatment between 2001 and 2015 were reviewed. Remission was defined as hypothyroid or euthyroid status without ATD, and with or without levothyroxine at 12 months after RAI therapy.
Results
The 1-year remission rate after 2nd RAI therapy (66%, 152/230) is significantly higher than that after 1st RAI therapy (48%, 393/815) or long-term ATD treatment after 1st RAI therapy failure (42%). The clinical response to 2nd RAI therapy was more rapid. The median time intervals from the 2nd RAI therapy to ATD discontinuation (1.3 months) and to the start of levothyroxine replacement (2.5 months) were significantly shorter than those for the 1st RAI therapy. A smaller goiter size, a longer time interval between the 1st and 2nd RAI therapies, and a longer ATD discontinuation period predicted remission after the 2nd RAI therapy. Finally, in 78 patients who failed the 2nd RAI therapy, the mean ATD dosage significantly reduced 5.1 mg over 12 months.
Conclusion
Repeated RAI therapy can be a good therapeutic option, especially in patients with smaller goiters and those who are more responsive to the 1st RAI therapy.

Keyword

Graves disease; Hyperthyroidism; Iodine radioisotopes; Iodine-131

Figure

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  Fig. 1. Clinical outcomes of radioactive iodine (RAI) therapy in Graves’ disease patients with antithyroid drug (ATD) failure. (A) Response for RAI therapy. (B) Cumulative remission rate within 1 year after each RAI therapy.

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  Fig. 2. Kaplan-Meier curves for antithyroid drug (ATD) discontinuation (A), and the start of levothyroxine (LT4) replacement (B) after each round of radioactive iodine (RAI) therapy among patients who achieved remission after the 1st RAI therapy (n=393) and 2nd RAI therapy (n=152).

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  Fig. 3. Change of antithyroid drug (ATD) dosage after radioactive iodine (RAI) therapy. (A) Change of ATD dosage in patients with persistent disease after each RAI therapy. (B) Patients who had persistent disease after 1st RAI therapy and received long-term ATD therapy were divided into two groups according to the 2nd RAI therapy, the 2nd RAI(+) and 2nd RAI(−) group. ATD dosage between two groups were compared, and ATD dosage in the 2nd RAI(+) group was significantly higher than that in the 2nd RAI(−) group between 3 and 12 months after 1st RAI therapy. aP<0.05 vs 2nd RAI(−) group at each time.

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