Endocrine Abstracts

Background: Amiodarone is a class-III antiarrhythmic agent used in chemical cardioversion for patients with atrial fibrillation. Due to its high iodine content, Amiodarone can cause thyroid dysfunction in patients with or without thyroid disease.

Clinical Case: 64-year-old lady presented with nausea, vomiting for a few weeks after starting Mounjaro, with tremors, heat intolerance, sweating, and lethargy. She has primary hyperparathyroidism, persistent atrial fibrillation refractory to electrical cardioversion/rate control, and was started on amiodarone 3 years ago. Bloods showed adjusted calcium of 2.97mmol/l, TSH <0.01mU/l, Free T4 >100pmol/l, negative TSH-stimulating immunoglobulins. She was treated for type 2 amiodarone-induced thyrotoxicosis (AIT), hypercalcaemia. Amiodarone and Colecalciferol were stopped, and she was started on Bisoprolol 2.5mg OD, Carbimazole 20mg BD. She had multiple re-admissions to hospital within a month with similar symptoms and shortness of breath with no improvement in her thyroid function tests. Echocardiogram showed normal biventricular systolic function. Neck ultrasound showed a diffusely bulky thyroid with multiple small hypoechoic nodules and normal vascularity, suggestive of thyroiditis. Carbimazole was stopped, and she was started on propylthiouracil 200mg TDS, prednisolone 30mg OD, cholestyramine 4grams ON, and lithium 400mg OD. Radioiodine was deemed inappropriate in her case due to previous use of amiodarone. In view of possible treatment resistance, she was referred to a tertiary centre for consideration of Iopanoic acid. Her symptoms and thyroid function have fortunately improved, with TSH <0.01 and free T4 of 27.8pmol/l after 2 months of quadruple therapy whilst waiting for Iopanoic acid. She was referred to the endocrine surgeons for thyroidectomy and parathyroidectomy.

Conclusion: Classification of AIT can be challenging in the acute setting due to the lack of clinical information. Colour flow Doppler ultrasonography is a useful tool to distinguish between type 1 and 2 AIT.