Amiodarone-induced thyrotoxicosis – do anti-thyroid drugs alone provide adequate treatment? (#236)
Introduction: Amiodarone-induced thyrotoxicosis (AIT) occurs in 3-12% of patients receiving amiodarone. There is a poor evidence base for treatment and limited data in an Australian population.
Objective: To compare the efficacy of antithyroid drugs (ATD) alone versus ATD and prednisone (ATD+PRED) in the treatment of AIT.
Methods: The pharmacological management of AIT using ATD alone versus ATD+PRED was reviewed in 25 patients, with the outcome being time to euthyroidism or thyroidectomy.
Results: There was a trend for baseline free thyroxine (fT4) level to be different between the treatment groups: ATD+PRED (n=9) 63.0 ± 11.0 pmol/l, ATD (n=11) 42.9 ± 8.0 pmol/l, no treatment (NIL, n=5) 25.2 ± 4.2 pmol/l, P=0.054. Of those treated initially with ATD, 6/11 (55%) required the addition of PRED due to inadequate response (n=5) or adverse event to ATD (n=1). Baseline fT4 was significantly higher in those ultimately treated with ATD+PRED (58.8 ± 8.3 pmol/l) compared to those treated with ATD or NIL (28.3 ± 3.1 pmol/l), P<0.01. In patients with fT4 <30 pmol/l, 75% (6/8) achieved euthyroidism without prednisone. There was a significant correlation between the initial dose of ATD and baseline fT4 level, r=0.54, P<0.01. Overall the baseline fT4 was higher in the group requiring thyroidectomy (n=9), 62 ± 13.8 pmol/l, compared to those not requiring surgery (n=16), 37.9 ± 3.9 pmol/l, P<0.05. In those not undergoing thyroidectomy, there was no difference in final time to fT4 normalisation between those receiving ATD+PRED (19.2 ± 3.3 weeks), ATD (15.6 ± 3.0 weeks) or NIL 18.8 ± 9.3 weeks. Of the 16 patients not undergoing thyroidectomy, 11 (69%) became euthyroid off all medication. One patient later died of multi-organ failure after a successful thyroid outcome.
Discussion: These data indicate that in patients with AIT, those with higher fT4 levels generally require glucocorticoids. The lack of difference in time to achieve euthyroidism between the groups is probably due to the greater disease severity in the group treated with ATD+PRED. Mild disease (fT4 <30pmol/l) can be successfully treated with ATD alone. Thyroidectomy in those responding poorly to medical therapy resulted in a uniformly good outcome.