Endocrine Abstracts

Introduction: About 3% of patients treated with amiodarone develop thyrotoxicosis (amiodarone induced thyrotoxicosis, AIT). Steroids and carbimazole are the main treatment options with surgical thyroidectomy performed in resistant cases. Radioiodine is believed to be unhelpful based on presumed poor radioiodine uptake by thyroid tissue saturated with iodine. We present a case of AIT with a low technetium uptake being successfully treated with radioiodine ablation.

Presentation: KA, a 63-year old caucasian male with paroxysmal atrial fibrillation and rapid ventricular rate was maintained on Amiodarone following failed ablation and alternative medical therapy. His baseline thyroid function was normal with a TSH of 1.36 and T4 of 18. After 30 months, he was found to be thyrotoxic with an undetectable TSH (<0.01) and free T4 of 82. He was treated with carbimazole and steroids with a diagnosis of type-2 AIT and amiodarone discontinued. Technetium uptake study of thyroid showed low uptake. Surgical thyroidectomy was contemplated but persistent tachycardia, hypotension and cardiac decompensation made him a poor surgical candidate. He was given 518 mBqI of radioiodine.

Progress: He became hypothyroid three months after radioiodine ablation (TSH: 38.5, T4: 9 and T3 3.1) and levothyroixine was introduced with careful titration. Once euthyroid, he underwent successful atrio-ventricular node ablation and has had no further tachyarrhythmia. He is currently maintained on 75 mcg of levothyroxine with a TSH of 1.0 and T4 of 18.

Discussion: There is near consensus amongst endocrinologists about the lack of efficacy of radioiodine ablation in AIT. A period off amiodarone of at least 6 months is also described as a requirement before radioiodine uptake into the thyroid is sufficient to make radioiodine therapy feasible. Successful radioiodine ablation of thyroid gland in our patient is contrary to these views and has the potential to widen treatment options available for AIT.