Distinct features of amiodarone-induced thyrotoxicosis

Amiodarone-induced thyrotoxicosis (AIT) is a challenging conditions for endocrinologists and cardiologists, differing in some important respects from the thyrotoxicosis of Graves disease and toxic multinodular goitre, a study in Sydney patients had concluded.The study reviewed a total of 149 patients seen at a single unit during 12 years. Mean TSH levels were suppressed to a similar extent in all three conditions. Free thyroxine (T4) levels were significantly higher in AIT and Graves disease than in patients with goitre. In contrast, free triiodothyronine (T3) levels were significantly higher in Graves disease than the other two conditions.There were six deaths, and all were in patients being treated with amiodarone for their atrial or ventricular arrhythmias. They were attributed to underlying diseases rather than anti-arrhythmic therapy: four were from intractable left ventricular dysfunction and two from multi-organ failure, one in a patient with end-stage renal disease and another with significant pulmonary fibrosis. The risk of death was not associated with thyroid hormone levels.AIT was more common in men than women, probably reflecting the prevalence of heart disease. Treatment was more difficult than for the other two forms of thyrotoxicosis. The average time to normalise free T4 levels was significantly longer, taking 28 weeks compared to 13 weeks for Graves disease and only eight weeks for multinodular goitre. Of 60 patients taking amiodarone, nine were treated with antithyroid medication plus corticosteroids. Eleven patients required thyroid surgery, three of whom also had plasmapheresis. The remainder were treated with carbimazole alone."Treatment of AIT is not straightforward," the report stated. "Because of the high iodine content of amiodarone and the low radioiodine uptake on scanning, radioiodine ablative radiotherapy in ineffective compared to other forms of thyrotoxicosis."The results emphasised the benefit of an echocardiogram in patients with AIT. If severe left ventricular dysfunction was present, then aggressive medication was needed and surgery should be considered earlier rather than later. Patients with moderate to severe LV dysfunction might require more intense monitoring of thyroid and cardiac function.Reference...