Long-term outcome of thyroid function after amiodarone-induced thyrotoxicosis, as compared to subacute thyroiditis

Background: Two main forms of amiodarone-induced thyrotoxicosis (AIT) exist: type 1 AIT is a condition of true hyperthyroidism developing in patients with pre-existing thyroid disorders, and usually requires thyroid ablative treatment. On the other hand, type 2 AIT is a form of destructive thyroiditis occurring in normal thyroids, the management of which usually consists in glucocorticoid treatment. Aim: To assess the long-term outcome of thyroid function in a prospective study of type 2 AIT patients, as compared to patients with De Quervain's subacute thyroiditis (SAT). Patients and Methods: Sixty consecutive patients with type 2 AIT were evaluated during oral glucocorticoid treatment (oral prednisone 30 mg/day, gradually tapered and withdrawn over a 3-month period) and followed for 38 4 months (range 672) thereafter. Sixty consecutive patients with SAT, referred to our Institutes during the same period and treated with the same therapeutic schedule, served as controls. Results: Type 2 AIT patients were older (p < 0.0001) and showed a larger male preponderance (M:F 3.6:1 vs 0.5:1, p < 0.0001) than SAT patients. Mean serum free T-4 (FT4) and free T-3 (FT3) concentrations at diagnosis were increased in both conditions, but higher in type 2 AIT than in SAT (FT4 47.6 +/- 18.8 and 29.6 +/- 8.3 pmol/l, respectively, p < 0.0001; FT3 15.4 +/- 7.0 and 11.2 +/- 3.0 pmol/l, respectively, p < 0.001). Correction of thyrotoxicosis was obtained in all patients in both groups, but restoration of euthyroidism occurred earlier in SAT than in type 2 AIT (p=0.006). Ten type 2 AIT patients (17%) and 3 SAT patients (5%, p < 0.03) became permanently hypothyroid after glucocorticoid withdrawal and required levothyroxine replacement. Conclusions: A relevant proportion of type 2 AIT patients develop permanent hypothyroidism after correction of thyrotoxicosis. Thus, periodic surveillance of thyroid status is required after type 2 AIT.