SAT469 Risk Factors for Relapse in Graves’ Disease and the Clinical Outcomes of Radioactive Iodine Treatment in Relapsed Cases

Disclosure: L. WingChing: None. X. Khor: None. F. Carter: None. Q. Ashcroft: None. V. Chandrabalan: None. P. M Joseph: None. Authors: Li Wing Ching, Xiao Ying Khor, Frederick Carter, Ashcroft Quinta, Vishnu Chandrabalan, Joseph Pappachan. Background: Relapse of Graves’ disease occurs in ≈50% of cases after the antithyroid pharmacotherapy. Identifying risk factors associated with relapse is crucial for planning treatment including radioactive iodine (RAI) ablation as well as to inform patients of probable clinical outcome following such treatment. Aims: (1) To identify the factors associated with relapse of Graves’ disease when the condition is first diagnosed. (2) To characterise the clinical outcomes and re-relapse rates after RAI treatment. Methods: Retrospective study of patients treated for Graves’ disease (with positive TSH-receptor antibodies [TRAb] >1.0 IU/L) between April 2004 and May 2021 at Lancashire Teaching Hospitals NHS Trust, UK. Demographic, clinical, laboratory, and treatment data were retrieved from prospectively maintained electronic health records. Data retrieved included known factors associated with high risk of relapse including markedly raised thyroid hormone (Free T4 [FT4] and/or Free T3 [FT3]), and TRAb levels. Outcome data after treatment was also analysed including the effects of RAI therapy such as hypothyroidism and time to its development, failure rate of first dose of RAI and its management. Results: Out of 1450 patients with Graves’ disease, 188 cases with meaningful study data receiving RAI ablation during the study period were analysed. The following factors (median (interquartile range/IQR) of relapsed vs non-relapsed) were associated with relapse requiring RAI ablation: TRAb levels - 10.3 (4.8-20.9) vs 5.1 (2.0-12.4) IU/L; p<0.001, FT4 - 56.7 (39.3 - 73.0) vs 42.6 (30.9-62.4) pmol/L; p<0.01, and FT3 - 24.4 (13.8 - 33.6) vs 16.2 (10.8-26.5) pmol/L; p=0.03. The median age at RAI ablation therapy was 48 (IQR 39-57.3) years with a female preponderance (140 [74.5%] cases). Radioactive Iodine-131 ((131)I) 555 MBq was used for treatment in all cases. 172 (91.5%) cases developed post-RAI hypothyroidism at a median follow up period of 3 (IQR: 2-11) months. RAI ablation failure occurred in 20 (10.6%) cases of whom 12 (60%) cases were successfully managed by RAI re-ablation, 5 (25%) cases preferred antithyroid pharmacotherapy, one (5%) underwent subtotal thyroidectomy and 2 (10%) cases refused treatment. Conclusions: Graves’ disease cases with high median levels of TRAb ≥10.3 IU/L, FT4 ≥56.7 pmol/L and/or FT3 ≥24.4 pmol/L at initial presentation are at high risk of relapse. RAI ablation should be offered to such patients as first-line treatment at initial presentation of the disease. Hypothyroidism occurs after RAI ablation in ≈92%. Chance of treatment failure with first RAI ablation procedure is only ≈11%. Presentation Date: Saturday, June 17, 2023