Endocrine Abstracts

Context: Amiodarone is a widely used anti-arrhythmic medication, however associated with a 15-20% rate of thyroid adverse effects. Amiodarone-induced thyrotoxicosis (AIT) is a complex disease due to diagnostic difficulties and therapeutic challenges. AIT patients often receive initial therapy for thyrotoxicosis before admission to a referral center. Whether the first-line medical therapy (i.e. therapies for thyrotoxicosis at first diagnosis of AIT) may affect the outcome of AIT patients is unknown.

Study design: Single-center historical-prospective cohort study of 313 AIT patients admitted to our university referral center for amiodarone-induced thyroid disorders.

Methods: Clinical and biochemical data at first diagnosis, at a referral center, and during the course of AIT were collected. The medical figures responsible for the first approach to the disease were recorded. Primary outcomes were cardiovascular (CV) events and hospitalizations. First-line therapies were appropriate when included glucocorticoids for type 2 AIT and methimazole for type 1 AIT at the approved dosage, either alone (optimal medical therapy, OMT) or in combination (right-dose combination therapy, RCT). Other therapies were considered not appropriate, including no therapy. Duration of exposure to thyrotoxicosis was the time from first diagnosis of AIT to its remission.

Results: 34.5% patients received appropriate therapy (28.1% OMT and 6.4% RCT), whereas non-appropriate therapies accounted for 65.6% of cases: specifically most patients originally approached by general practitioners and cardiologists received no therapy at all (56.9% and 50% respectively), whereas inappropriate therapies for the AIT-type (i.e. glucocorticoids for type 1 AIT and methimazole for type 2 AIT) was the most common therapy for patients originally approached by endocrinologists outside the referral center. CV events, and hospitalizations were more frequent in patients who received non-appropriate therapies (33.2% vs 4.5%, and 24.9% vs 6.5%, respectively; P<0.0001 for both). Appropriate therapies reduced serum thyroid hormone concentrations (P=0.018) at variance with non-appropriate therapies. The duration of exposure to thyrotoxicosis was longer in patients receiving non appropriate therapies and was a risk factor for arrhythmias (HR 1.004, P=0.0008), MACEs (HR 1.004, P=0.020) and hospitalizations (HR 1.006, P<.0001).

Conclusions: The first medical therapy of AIT influences the exposure to thyrotoxicosis and the occurrence of cardiovascular events and hospitalizations.