Amiodarone-induced thyroid dysfunction in Taiwan: a retrospective cohort study.

Background: The incidence and risk factors of amiodarone-induced thyroid dysfunction are variable in the literature.
Objective: The aim of this study was to investigate the clinical and biochemical features and risk factors of amiodarone-induced thyroid dysfunction in Taiwan.
Setting: This study was conducted at a tertiary referral center for arrhythmia.
Method: Retrospective analysis of patients treated with amiodarone during the years 2008-2009 was performed.
Main Outcome Measure: Incidence and risk factors of amiodarone-induced thyrotoxicosis (AIT) and amiodarone-induced hypothyroidism (AIH) were assessed.
Results: Of the 527 patients, 437 (82.9 %) remained euthyroid, 21 (4.0 %) developed AIT, and 69 (13.1 %) were affected with AIH. In univariate analysis, AIT was associated with younger age, and the risk factors for AIH included older age, higher baseline thyroid stimulating hormone (TSH) titer, lower baseline free T4 level, lower cumulative amiodarone dosage, and shorter amiodarone treatment duration. Cox regression analysis was performed to determine the different risk categories in the elderly population of age 65-74 (young-old), 75-84 (old-old), and ≥85 years old (oldest-old). Additionally increased risk of AIH was found in the groups of old-old (HR 2.09, 95 % CI 1.11-3.96) and oldest-old (HR 2.57, 95 % CI 1.21-4.75). In the multivariate analysis of risk factors for AIH, baseline TSH level (HR 1.38, 95 % CI 1.12-1.70) and cumulative amiodarone dosage (HR 0.95, 95 % CI 0.93-0.97) remained statistically significant.
Conclusion: AIH was much more common than AIT in Taiwan, an area with sufficient iodine intake. Higher baseline TSH level was the predominant independent risk factor for the development of AIH.