SPECTRUM OF THYROID DISORDER IN AMIODARONE-INDUCED DYSFUNCTION - A CASE REPORT

Abstract

INTRODUCTION
Amiodarone is the most commonly used anti-arrhythmic drug worldwide. It can lead to both hypothyroidism (amiodarone-induced hypothyroidism, AIH) and less commonly, hyperthyroidism (amiodarone-induced thyrotoxicosis, AIT). While AIH is more common in iodine-sufficient populations, AIT is seen more frequently in iodine-deficient areas.

CASE
A 53-year-old man had hyperthyroidism and subsequently had hypothyroidism following amiodarone treatment. He had underlying non-ischaemic cardiomyopathy with recurrent ventricular tachycardia requiring ICD insertion in 2008. He was dependent on amiodarone for a few years in view of recurrent ventricular tachycardia, despite having two cardiac ablations. Initially, he developed hyperthyroidism following amiodarone treatment and was started on Carbimazole. Subsequently, he became hypothyroid. Clinically, he was euthyroid with no palpable goiter. Anti-thyroid stimulating hormone (TSH) receptor antibody was undetectable. Ultrasonography of the thyroid revealed normal thyroid gland with reduced vascularity. Thyroid uptake scan showed a hypofunctioning thyroid gland. Based on his series of thyroid function tests, he had AIT type 2 and subsequently developed overt AIH. We noticed, however, that the patient had elevated free thyroxine (FT4) with high TSH and was asymptomatic for 3 months duration while still on amiodarone. Upon review one year later, he currently has subclinical hypothyroidism.

CONCLUSION
This case illustrates the spectrum of thyroid function abnormalities in patients on amiodarone. In the absence of hypothyroid symptoms or thyroid antibodies, patients with moderately elevated serum TSH (<20 mIU/L) but high-normal or raised serum FT4 may reflect amiodaroneinduced alteration in thyroid function parameters or subclinical hypothyroidism. Therefore, thyroid function test results while on amiodarone should be scrutinized before definitive treatment is instituted. A baseline evaluation will help identify patients who may be predisposed to developing thyroid dysfunction while on amiodarone.