Amiodarone-induced thyrotoxicosis responding to oral steroid therapy.

Sir, Amiodarone-induced thyrotoxicosis is well known for being difficult to treat. Thionamide drugs often fail,' and if possible amiodarone should be stopped. Recently there has been much work and discussion on the use of thionamides combined with potassium perchlorate, and the use of corticosteroids in the treatment of this condition. A 49 year old man presented to clinic having lost 2 stones in weight over a 2 week period. This was associated with watery diarrhoea, heat intolerance and feeling tremulous. Three years earlier he had had an aortic valve replacement and triple by-pass graft followed by amiodarone therapy 400 mg daily. He had a smooth goitre, a pulse of 95 sinus rhythm, a proximal myopathy, and laboratory results confirmed thyrotoxicosis. Free thyroxine (T4)> 126 pmol/I (normal range 10-30 pmol/l). Total T4> 320 nmol/l (normal range 56-154 nmol/1). Serum triiodothyronine (T3) = 5.4 nmol/l (normal range 1.1-2.8 nmol/l). Serum thyroid stimulating hormone (TSH)< 0.1 mU/I (normal range 0.5-5.0 mU/l). A diagnosis ofamiodarone induced-thyrotoxicosis was therefore made. Carbimazole 45 mg/day was commenced. Amiodarone was withdrawn. After one month T4 remained >320 nmol/l and prednisolone 30mg daily was commenced. Within 2 weeks T4 became measurable at 260 nmol/l. Prednisolone was then decreased to 20 mg daily, and carbimazole to 30 mg/day. Within 8 weeks all indices had returned to normal. Prednisolone and carbimazole were slowly reduced over the next 4 months to zero and biochemical euthyroidism persisted. Recent work has focused on the efficacy of a thionamide drug combined with potassium perchlorate2 although the rapidity of the response has been questioned.3 Corticosteroid therapy has been widely advocated4'5 often seemingly being effective where other therapies have failed. This case report serves to further underline this message. One month of treatment with carbimazole proved fruitless whilst after 2 weeks of oral prednisolone the patient's hyperthyroidism had turned the metaphorical corner. Three months elapsed between diagnosis and cessation of amiodarone, and attaining biochemical euthyroidism. Spontaneous cure for this condition has been quoted as occurring within an average of 6 months.4 The shorter remission period here and its striking relation to commencement of prednisolone therapy argue against this being a spontaneous cure.