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Radioactive Iodine for the Treatment of Subclinical Thyrotoxicosis Grade 1 and 2: Outcome of up to 18-Year Follow Up

Lookup NU author(s): Jason Phowira, Nicholas Vennart, Dr Jolanta Weaver



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Copyright © 2022 Phowira, Coffey, Bartholomew, Vennart, Moreira, Emerson, Kennedy and Weaver. Background: Subclinical thyrotoxicosis (SCT) is associated with significant morbidity and mortality, specifically increased risk of atrial fibrillation and cardiovascular death. The management is ill-defined due to the scarcity of randomised controlled studies. Some clinicians recommend radioiodine (RAI) treatment however its long-term outcome is unknown. Therefore, further data is needed to provide robust evidence-based guidelines. Methods: A prospective, single-protocol analysis of the outcome of SCT patients (Grade 1; 0.1-0.4 mIU/L and Grade 2; <0.1 mIU/L) treated with mean dose of 427 MBq of I131, followed up for up to 18 years. Thyroid function tests were measured at 4-6 weeks, 3-, 6-, and 12-months post-RAI, and annually thereafter. Cure was defined as achieving a euthyroid/hypothyroid state. Results: Seventy-eight patients with a median age of 68 years (range 36-84) and varying aetiology [55 toxic multinodular goitre (TMNG), 10 toxic nodule (TN) and 13 Graves’ disease (GD)] were followed up for a median period of 7.5 years (range 1-18). The cure rate was 100%. The rates of hypothyroidism in TMNG, TN and GD were 23.6%, 30% and 38.5% respectively. The median time to hypothyroidism was 6 and 12 months in GD and TMNG/TN respectively. No differences in outcome between Grade 1 versus Grade 2 were observed. Conclusion: RAI using single mean dose of 427 MBq is effective and safe, irrespective of aetiology or grade of TSH suppression. GD patients become hypothyroid within the first year, whilst TMNG/TN for up to 9-years. Thus after 12 months of follow up, annual thyroid function monitoring is advised.

Publication metadata

Author(s): Phowira J, Coffey KL, Bartholomew PH, Vennart N, Moreira M, Emerson H, Kennedy D, Weaver JU

Publication type: Article

Publication status: Published

Journal: Frontiers in Endocrinology

Year: 2022

Volume: 13

Online publication date: 09/03/2022

Acceptance date: 07/02/2022

Date deposited: 21/04/2022

ISSN (electronic): 1664-2392

Publisher: Frontiers Media S.A.


DOI: 10.3389/fendo.2022.843857


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