A case of amiodarone-induced hypothyroidism

Abstract

A sixty-four-year old lady with a past medical history of total thyroidectomy for Graves’ disease and atrial fibrillation on amiodarone was referred to the endocrine out-patients in view of hypothyroidism. Since starting amiodarone, the TSH was noted to be elevated at 75 mU/l and the free T4 was 18 pmol/l. The patient complained of non-specific lethargy and was administered levothyroxine 50 mcg daily. Despite this her TSH remained elevated at 147 mU/l with a free T4 of 17.3 pmol/l and a free T3 of 2 pmol/l. TSH interference was ruled and a pituitary profile was normal. In the time of 2 years, despite gradual augmentation of her levothyroxine dose, the TSH remained elevated. At this point it was suspected that amiodarone might be causing type 1 5’ deiodinase enzyme inhibition leading to reduced peripheral conversion of T4 to T3. Hence the patient was commenced on a trial of liothyronine 12.5 mcg twice a day in addition to her levothyroxine. This eventually resulted in normalization of her thyroid function tests. Amiodarone induced hypothyroidism highlights the importance of life long thyroid function monitoring (free T3, free T4 and TSH) in patients on amiodarone. This case of amiodarone-induced hypothyroidism also reveals another possible indication for levothyroxine/liothyronine combination therapy.