(14.12) Amiodarone Induced Thyrotoxicosis- Use of Color Flow Doppler Sonography in Differentiating Type 1 AIT vs Type 2 AIT. A case Series

Patients treated with Amiodarone for a cardiac arrythmia may develop Amiodarone-induced thyrotoxicosis (AIT). Color flow Doppler sonography (CFDS) is a technique that shows intrathyroidal blood flow and provides real-time information on thyroid morphology and hyperfunction. We present two cases of patients with AIT where we were able to quickly differentiate type I and type II using CFDS.

Case(s) Description :

Case 1: A 75-year-old male with paroxysmal atrial fibrillation (AF) treated with Amiodarone, presented with new onset hyperthyroidism. Patient had a cardioversion in 2020 and was placed on amiodarone for maintenance of sinus rhythm. After a year, he was discontinued on Amiodarone but unfortunately, he converted back into AF. Amiodarone was restarted but after a few weeks, he developed rapid unintentional weight loss (2Lb weight loss per week). A TSH showed 0.007 (reference range:0.550-4.780 uIU/mL); free T4 of 5.37 (reference range:0.89-1.76 ng/dL). His thyrotrophin receptor antibody and thyroid stimulating hormone were both negative. Methimazole 10mg twice daily was started. A CFDS showed slight hypervascularity with a slightly enlarged thyroid but without nodules. AIT I was diagnosed. Methimazole was increased to 10mg three times daily. On a one month follow up, there was already improvement in his free T4 of 3.35 (reference range:0.89-1.76 ng/dL).

Case 2: A70-year-old male with history of paroxysmal atrial fibrillation on amiodarone, who presented with acute onset of shortness of breath. ECHO showed reduced ejection fraction of 20%. TSH was 0.05mIU/L (Reference range 0.465-4.68 mIU/mL), free T4 of 3.78μg/dL (Reference range 0.78-2.19 ng/dL). Patient reports weight loss of 18 pounds in the last 2 months. Amiodarone was started three and a half years prior. Autoantibody testing for thyroid disease including Anti-Thyroid Peroxidase, anti-thyroglobulin antibody and thyrotropin receptor antibody were negative. He was started on prednisone 30 mg daily and methimazole 10 mg daily for amiodarone induced thyrotoxicosis. A CFDS showed the absence of hypervascularity and normal thyroid. Methimazole was discontinued prior to hospital discharge and he was continued on Prednisone 30 mg. Repeat labs a month later while on prednisone 30 mg showed normalization of thyroid hormones with a TSH of 0.8, free T4 of 1.38.The prednisone was tapered and stopped a month later, for a total of two months of treatment. 

Discussion :

CFDS is a useful and fast diagnostic tool in differentiating between AIT I and AIT II. This rapid differentiation is useful clinically to help guide clinicians on what therapies to provide.