Endocrine Abstracts

Introduction: Amiodarone is an antiarrhythmic iodine-rich drug, known to induce thyroid dysfunction both due to its high iodine content and through amiodarone-induced thyrotoxicosis (AIT), being this latter process classified into three different types. Type 1 is associated with increased thyroid hormone synthesis; type 2 is a destructive process with thyroid hormone release and type 3 is thought to be a mixture of the former two. Since treatment options are different, there has been a growing need for a diagnostic method that could accurately distinguish these types and therefore allow targeted therapy. 99mTc-sestamibi scintigraphy has been gaining a specific role in this matter: with recognized increased uptake by epithelial cells that show high mitochondrial concentration, it allows the physician to visually differentiate between necrotic or destroyed tissue (which shows absent or very low uptake of the radiopharmaceutical) from hypermetabolic cells (with increased uptake).

Case report: A 72-year-old male with atrial fibrillation treated with amiodarone for 10 years was sent to our Endocrinology outpatient clinic for new-onset asymptomatic subclinical hyperthyroidism (FT3 2.56 pg/ml (2.00 4.40); TT3 85 ng/dl (80–200); FT4 1.59 ng/dl (0.93–1.70); TT4 10.0 (5.1–14.1); TSH 0.03 mU/l (0.27–4.20)). He had a history of euthyroid benign nodular disease. We admitted AIT type 2, but considering the mild thyroid dysfunction, we chose to pursue further evaluation with 99mTc sestamibi scintigraphy, in order to initiate targeted therapy. Scintigraphic images showed initial uptake by the thyroid gland with rapid washout, a pattern described in literature as corresponding to AIT type 3. The patient’s thyroid hormones normalized before starting any medication and he is currently on follow-up.

Conclusion: This case report is illustrative of the possible role of 99mTc sestamibi scintigraphy in diagnosis and management of thyroid disfunction induced by amiodarone. However, more expertise is further needed.