Amiodarone-Induced Thyrotoxicosis After Total Thyroidectomy for Metastatic Follicular Thyroid Cancer

ABSTRACT Objective To describe the case of a man who developed amiodarone-induced thyrotoxicosis (AIT) after a total thyroidectomy for metastatic follicular thyroid cancer because of the effect of the drug on metastasis. To the best of our knowledge this is the first reported case of this condition. Methods We completed a retrospective review of medical records and laboratory results including thyroid function tests as well as imaging reports including plain radiographs, positron emission tomographs, computed tomographs, and histology reports. Results A 78-year-old man had undergone a total thyroidectomy for follicular thyroid cancer. He had meta-static disease in his chest and vertebrae, and after the operation he was started on suppressive levothyroxine treatment prior to ablative radioactive iodine treatment. Prior to thyroidectomy, his thyroid-stimulating hormone (TSH) concentration was 3.21 mU/L (reference range is 0.35 to 3.50 mU/L). On suppressive thyroxine replacement, his TSH concentration was 0.02 mU/L, his free thyroxine was 13 pmol/L (reference range is 8 to 12 pmol/L), and free triiodothyronine was 5.8 pmol/L (reference range is 3.8 to 6.0 pmol/L). He subsequently had a myocardial infarction and required antiarrhythmic treatment with amiodarone. Eleven days later he developed the clinical and biochemical features of thyrotoxicosis (TSH <0.01 mU/L, free thyroxine of 41 pmol/L, and free triiodothyronine of 14.7 pmol/L). His thyroxine dose was reduced and then discontinued 3 days later. AIT was the principal differential diagnosis, but before being able to determine the nature of the condition he died 18 days after his myocardial infarction. Conclusion AIT can still occur after total thyroidectomy if metastatic tissue is present.