Endocrine Abstracts

Introduction: Definitive treatment of hyperthyroidism with Radioactive Iodine (RAI) ablation therapy has been associated with weight gain from RAI induced hypothyroidism. Literature on weight data of post-RAI patients following normalisation of thyroid function is equivocal.

Objective: We undertook a retrospective study to evaluate the effect of RAI on weight in Hyperthyroid patients in University Hospitals of Leicester NHS Trust (UHL).

Methods: Retrospective electronic records review on ‘Clinical Workstation’ database was undertaken to identify RAI-treated patients. We limited the electronic search to adults (>16 years old) who received at least one session of RAI for hyperthyroidism at UHL from 2003 to 2022. We only included patients with measured weight in the euthyroid state before and after RAI. We excluded patients with thyroid carcinoma due to direct effect of cancer on weight regardless of thyroid function. Euthyroid state was defined as normal thyroid function test and/or absence of clinical features of hyper/hypothyroidism at the time of body weight measurement.

Results: Of the 575 patients undertaken RAI treatment, n= 51 patients were included to analyse as they fulfilled the criteria; a) had pre- and post-RAI weight data within 4-weeks of clinical encounter, and b) TSH normal. Majority were females (Female:Male=42:9). Mean age=57 years. Aetiology was Graves’ disease in 20, Non-autoimmune in 31 patients. Mean duration of follow up was 52 months. All 51 patients were rendered euthyroid on anti-thyroid medications (ATDs) prior to definitive treatment with RAI. Mean weight gain was 4.02 kg (5.3%) following RAI treatment. Autoimmune hyperthyroidism patients gained 3.05 kg (4.2%) compared to 4.65 kg (6%) in the non-autoimmune group. Males appear to have gained more weight than females following RAI, 7.56 kg (8.2%) and 3.26 kg (4.5%), respectively.

Discussion: RAI appears to cause weight gain across gender and age groups. However, weight documentation during clinical encounters has been inconsistent. This study did not account for confounders like lifestyle, co-morbidities and medications that potentially impacted body weight and finally, it’s unclear if there’s an element of weight overcorrection prior to TSH normalisation from hypo/hyperthyroidism. We took findings of this study to set up a prospective cohort study looking for RAI impact on body weight across aetiologies, interventions (ATDs, surgery and RAI) and comorbidities.

Learning points: 1. RAI treatment appears to cause weight gain across gender and age categories.

2. Patient information leaflet warning of potential weight gain side effect ahead of RAI treatment may influence treatment choice and help adopt preventative dietary and life-style measures.