Proportion of type 1 and type 2 amiodarone-induced thyrotoxicosis has changed over a 27-year period in Italy

Context Two main forms of amiodarone-induced thyrotoxicosis (AIT) exist. Type 1 AIT is a form of iodine-induced hyperthyroidism. Its management is complex and includes thionamides, potassium perchlorate and, occasionally, thyroidectomy. Type 2 AIT is a destructive thyroiditis, responds to glucocorticoids, and usually does not require further thyroid treatment once euthyroidism has been restored.

Objective To assess retrospectively the prevalence and relative proportion of type 1 and type 2 AIT over a 27-year period at a tertiary referral centre in Italy.

Patients Consecutive AIT patients (n = 215) seen at the department of endocrinology of the University of Pisa between 1980 and 2006.

Results Type 1 AIT constituted the most frequent AIT form (60%) during the first years covered by this study. The annual mean number of type 1 AIT patients was 3·6 at the beginning of the study period, and 2·5 during the later years. In contrast, the mean annual number of new cases of type 2 AIT progressively increased from 2·4 to 12·5. Likewise, the proportion of type 2 AIT increased in a significant linear manner (P < 0·0001), currently accounting for 89% of AIT cases. Type 2 AIT patients showed a male preponderance, higher serum FT4/FT3 ratio (P < 0·002), lower 3-h and 24-h thyroidal radioactive iodine uptake values (P < 0·0001), and received a higher cumulative dose of amiodarone (P < 0·0001) than type 1 AIT patients.

Conclusions Over a 27-year period, the epidemiology of AIT changed, as the prevalence of type 2 AIT progressively increased and that of type 1 remained constant. Thus, under most circumstances, endocrinologists nowadays deal with type 2 AIT, which is a destructive thyroiditis, generally treated successfully with glucocorticoids. Although no additional treatment is usually required after the destructive process subsides, periodic assessment of thyroid function is warranted, because of the occurrence of hypothyroidism (up to 17%) during long-term follow-up of these patients.