Diagnosis and management of amiodarone-induced thyrotoxicosis: similarities and differences between North American and European thyroidologists.

Objective: To investigate how North American thyroidologists assess and treat amiodarone-induced thyrotoxicosis (AIT) and to compare the results with those of the same questionnaire-based survey previously carried out among European thyroidologists.

Design: Members of the American Thyroid Association (ATA) with clinical interests were sent by e-mail a questionnaire on the diagnosis and management of AIT, 115 responses were received from the United States and Canada, representing about one-third of ATA members with clinical interests.

Results: The majority of respondents (91%vs. 68% in Europe, P < 0.05) see < 10 new cases of AIT per year, and AIT seems less frequent than amiodarone-induced hypothyroidism (AIH) in North America (34% and 66% of amiodarone-induced thyroid dysfunction, respectively, vs. 75% and 25%, respectively, in Europe, P < 0.001). When AIT is suspected, in North America hormonal assessment is mostly based on serum free T4 (FT4) and TSH measurements, while serum free T3 (FT3) determination is requested less frequently than in Europe; thyroid autoimmunity is included in the initial assessment less than in Europe. Most commonly used additional diagnostic procedures include, as in Europe, thyroid colour-flow Doppler sonography, and to a lesser extent, thyroid radioactive iodine uptake and scan, but Europeans tend to request multiple tests more than North Americans. Withdrawal of amiodarone is more often considered unnecessary by North American thyroidologists (21%vs. 10% in Europe in type 1 AIT, P < 0.05, 34%vs. 20% in type 2 AIT, P < 0.05). In type 1 AIT thionamides represent the treatment of choice for North Americans as well as for Europeans, but the former use them as monotherapy in 65%vs. 51% of Europeans (P < 0.05) who more often consider potassium perchlorate as an useful addition (31%vs. 15% of North Americans, P < 0.01). Glucocorticoids are the selected treatment for type 2 AIT, alone (62%vs. 46% in Europe, P < 0.05) or in association with thionamides (16%vs. 25% in Europe, P = NS). After restoration of euthyroidism, thyroid ablation in the absence of recurrent thyrotoxicosis is recommended in type 1 AIT less frequently by North Americans. If amiodarone therapy needs to be reinstituted, prophylactic thyroid ablation is advised by 76% in type 1 AIT, while a 'wait-and-see' strategy is adopted by 61% in type 2 AIT, similar to behaviour of European thyroidologists.

Conclusion: Similarities and differences exist between expert North American and European thyroidologists concerning the diagnosis and management of AIT. While differences reflect the frequent uncertainty of the underlying mechanism leading to AIT, similarities may represent the basis to refine the diagnostic criteria and to improve the therapeutic outcomes of this challenging clinical situation.