Amiodarone-Induced Thyroid Dysfunction: A Rare Adverse Effect

Background: Amiodarone is a widely prescribed class III antiarrhythmic drug used for the management of atrial and ventricular arrhythmias. Despite its effectiveness, long-term therapy may lead to thyroid dysfunction because of its high iodine content and direct effects on thyroid tissue. Amiodarone-induced thyrotoxicosis is an uncommon but clinically important adverse effect that requires early recognition and management. Case Presentation: A 68-year-old male with persistent atrial fibrillation receiving amiodarone 200 mg daily for three years presented with fatigue, palpitations, excessive sweating, heat intolerance, tremors, and significant weight loss. Laboratory investigations revealed suppressed thyroid-stimulating hormone levels with elevated free thyroxine and free triiodothyronine levels. Thyroid autoantibodies were negative, and Doppler ultrasonography demonstrated reduced thyroid vascularity, suggestive of Type 2 amiodarone-induced thyrotoxicosis. Amiodarone was discontinued, and treatment with oral prednisolone and beta-blocker therapy was initiated. The patient showed progressive clinical and biochemical improvement, achieving complete recovery during follow-up. Conclusion: This case emphasizes the importance of regular thyroid monitoring in patients receiving long-term amiodarone therapy to facilitate early diagnosis and prevent serious complications.