7179 Efficacy of radioactive iodine for the treatment of thyrotoxicosis in a prospective cohort in Aotearoa/New Zealand

Abstract Disclosure: J. Tamatea: None. S. Nottingham: None. V. Boyle: None. M.S. Elston: None. Background – The outcome following treatment of thyrotoxicosis with a single fixed-dose radioiodine (RAI) can be difficult to predict and has been shown to have a lower success rate in Māori vs. non-Māori (1).Aim – the aim of this prospective study was to compare RAI treatment outcomes between Māori and non-Māori, identify factors that are associated with RAI treatment failure in thyrotoxicosis and whether these factors affect the difference in ethnicity outcomes seen.Method – all patients over the age of 16 years referred to Waikato Hospital (Hamilton, New Zealand) for the treatment of thyrotoxicosis with RAI between March 2013 and February 2015 were invited to participate in this study. Demographic information was collected with a questionnaire prior to treatment. Aetiology and severity of thyrotoxicosis at time of diagnosis was retrospectively collected. Laboratory investigations, ultrasound thyroid volume and thyroid pertechnetate uptake were carried out prior to RAI treatment. Participants were followed up for12 months after RAI to assess outcome to treatment. Univariate analysis of variables were carried out for the full cohort and for Graves’ Disease (GD) cohort. Logistic regression analysis was carried out including ethnicity and additional variables of age, gender, diagnosis, thyroid volume, smoking status, and BMI.Results – a total of 162 participants were included: 71 identified as Māori and 91 as non-Māori. At 12 months follow up, 146 participants (90.1%) had a successful treatment outcome follow a single dose of RAI. Successful outcome was achieved in 85.9% of Māori vs 93.4% of non-Māori (p = .113), however when only looking at the GD cohort, Māori were less likely to have successful outcome than non-Māori (68.75% vs 89.4% p = .022). Following regression analysis ethnicity was no longer a variable associated with treatment failure. When controlling for other variables, factors found to increase the risk of failing RAI were diagnosis of TMNG/STA (OR 0.03; 95%CI 0.002-0.035), larger thyroid volumes (OR 1.04; 95%CI 1.01 - 1.07 per mL of thyroid volume) and smoking (OR 6.71; 95%CI 1.2 - 37.4 for current smokers).Conclusion - RAI is an effective definitive treatment option for thyrotoxicosis. Factors found to be associated with treatment outcome are aetiology of thyrotoxicosis, thyroid volume, and smoking status. These factors likely explain the ethnicity difference in treatment outcome following RAI in Māori vs non-Māori.References – 1. Tamatea JAU, Conaglen JV, Elston MS. Response to Radioiodine Therapy for Thyrotoxicosis: Disparate Outcomes for an Indigenous Population. International Journal of Endocrinology. 2016;2016:7863867. Presentation: 6/2/2024