Clinical experience of amiodarone-induced thyrotoxicosis over a 3-year period: role of colour-flow Doppler sonography

Objective Current thinking is that amiodarone-induced thyrotoxicosis (AIT) might be either iodine-induced thyrotoxicosis in latent hyperthyroidism (Type 1) or destructive thyroiditis (Type 2), and also that colour-flow Doppler sonography (CFDS) of the thyroid and serum interleukin 6 (IL-6) are tools that can classify AIT and direct treatment. To assess the validity of this thinking, our objective was to determine whether CFDS and IL-6 identified AIT subgroups with distinct features. Design Retrospective case-note audit of all patients presenting with AIT to the Endocrine Department of a UK teaching hospital over a 3-year period. To assess proportions of Type 1 vs. Type 2 AIT and to compare and contrast their clinical features. Patients 37 patients were identified with AIT (mean age 65, range 20-86 years). In 30 patients in whom AIT persisted, 25 underwent CFDS. Results In 25 patients who underwent CFDS, 10 (40%) were classified as Type 1, 10 (40%) as Type 2 and 5 (20%) as indeterminate type. In the patients classified by CFDS in whom AIT persisted, 40% of Type 1 patients were male vs. 90% of Type 2 patients. Also, free T4 tended to be lower in patients presenting with Type 1 AIT (52.1+/-7.5 pmol/l) compared to Type 2 (74.8+/-8.1 pmol/l, P=0.08), free T3 was lower (8.8+/-0.9 vs. 15.6+/-3.0 pmol/l, P=0.03) and the cumulative amiodarone dose was lower (66+/-20 vs 186+/-28 g, P=0.002). We used less prednisolone to achieve euthyroidism in patients with Type 1 AIT whereas carbimazole doses were not different and the time to euthyroidism was the same in both groups (81 21 vs. 88 13 days). IL-6 was raised in two patients with Type 1 and in one patient with Type 2 AIT. Conclusions CFDS could characterize two distinct subtypes in patients with AIT. Conversely, IL-6 seemed to be an unhelpful test in this context.