Endocrine Abstracts

Introduction: AIT1 usually occur on a background of Graves’ disease or toxic nodule goitre. The disease usually requires higher doses of carbimazole than Graves’, might need rescue thyroidectomy, and can be treated with radioiodine with higher than standard radioiodine doses after iodine contamination has come down.

Case Presentation: 57-year-old gentleman with history of HTN, T2DM, dyslipidemia, aortic stenosis, recurrent paroxysmal atrial flutter, previous multiple DC cardioversions and multiple amiodarone loading. He had an ablation procedure on March 2021, was symptom-free for nearly one year. Got readmitted with a new AF and was treated with intravenous amiodarone followed by cardioversion. He was referred to endocrine for new onset hyperthyroidism: TSH 0.04, FT4 34.6, noted within few days of receiving amiodarone. TFT’s prior to this were normal. No evidence of thyroiditis, goitre, or thyroid eye disease. TRAb: negative. US thyroid: no nodules, normal vascularity. Pertechnetate scan: normal uptake. Commenced on carbimazole with diagnosis of AIT1 on normal thyroid, requiring 40-60mg up to week-20. Patient didn’t receive steroids. FT4 levels were 50.6 (week-6), 50.8 (week-10), 38.2 (week-16), and 21.9 (week-20). Carbimazole reduced from this time. Received 602 MBq radioiodine in Jan 2023 (11-months post-diagnosis). From June 2023 developed overt hypothyroidism and is on levothyroxine.

Discussion: Points supporting AIT1: rapid onset thyrotoxicosis after amiodarone, progressive increase in FT4 despite higher carbimazole doses. AIT1 should receive carbimazole until euthyroidism, and thereafter definitive therapy with RAI or thyroidectomy. Time elapsed from initiation of amiodarone and occurrence of thyrotoxicosis is much shorter in AIT1 than AIT2. As iodine-replete thyroid of AIT is less responsive to thionamides, very high carbimazole doses for longer periods are needed before restoring euthyroidism. In iodine-replete patients on amiodarone, absent RAIU is invariably found in all. Standard US has low diagnostic value in AIT. CFDS provides a non-invasive assessment of vascularity.