Endocrine Abstracts

Background/Aim: Radioactive-iodine (RAI) therapy aims to cure hyperthyroidism, with some International authorities recommending a sufficient RAI dose to render patients hypothyroid. An audit on low dose RAI (<400 MBq) at our University Hospital in 2014 suggested above national average rates of Thyrotoxicosis relapse (24%) and lower rates of hypothyroidism (41%) 6-months post RAI. From 2015, a fixed dose (555 MBq) RAI was utilised and we present the audit outcomes using this 555MBq dose.

Methods: Demographics, clinical and biochemical data on all patients at our Hospital who received 1st dose of RAI for hyperthyroidism in the year 2015 was obtained (n=69). Thyroid status at 6 weeks, 3–6 months and 12 months was determined to analyse the rates of relapse and Hypothyroidism post RAI.

Results: Demographics of cohort: Age 54.5±13.8 (mean±S.D.) years; Caucasians 90%; Females 78%; Graves’ disease 70%; Pre-existing TED 10%. RAI was used as primary treatment in 5.8% and others post ATD treatment with mean duration 13.6 months. Mean duration of thyrotoxicosis 45.2±41.1 months. The proportion with relapse of Thyrotoxicosis and those who developed hypothyroidism at 6 months were 15.5 and 55.2% respectively. On retrospective analysis, among patients who were thyrotoxic at 6 months (15.5% of n=58 with 6 months data), their status at 6 weeks post RAI review were: Euthyroid 22.2%, Hypothyroid 0%, Subclinical Hypothyroid 0%, Subclinical Thyrotoxic 11.1% and Thyrotoxic 66.7%. Of patients who were thyrotoxic at 12 months (8.3% of n=36 with 12 months data), 100% were Thyrotoxic at 6 months post RAI. On logistic regression neither demographics nor biochemical parameters predicted Thyrotoxicosis relapse at 6 or 12 months post RAI.

Conclusion: Standardisation of RAI dose to 555 MBq for treatment of hyperthyroidism improved cure rates of hyperthyroidism, reducing the risk of relapse of thyrotoxicosis and with higher hypothyroidism rates. The incidence of transient Eu/Hypothyroid state post RAI progressing to overt Thyrotoxicosis was low with 555 MBq.