Unusual course of Amiodarone-induced hypothyroidism: case report
M. Motyka, M. Kostecka-Matyja, D. Pach & A. Hubalewska-Dydejczyk
Introduction: Amiodarone a potent antiarrhythmic medication induces thyroid dysfunction in about 20% of patients. Amiodarone-induced hypothyroidism (AIH) usually occurs early in the course of treatment, more often in iodine-sufficient areas, in women, and in the presence of thyroid autoantibodies. Long-term treatment with amiodarone is associated with a reduction in prevalence of AIH, which may reflect adaptation of the thyroid autoregulatory mechanisms to iodine excess.
Case report: A 68-year-old man referred to our outpatient clinic with a history of myocardial infarction, CABG, hypertension, and ventricular extrasystoles (Lown class IVb). He had been treated with amiodarone for the past 8 years. His thyroid hormone status had been checked in regular 6-month intervals showing normal TSH, FT4, FT3 concentrations. However, the last results were as follows: TSH- 33.7 mIU/l, FT4- 13.9 pmol/l (12.422.0), FT3- 4.7 pmol/l (2.65.7), thyroid autoantibodies assays were negative. He was then started on 50 μg of levothyroxine and amiodarone was discontinued shortly after, as cardiologists considered it safe. For the next one year patient still required substitution with the same dose of levothyoxine and his TSH and FT4 concentrations returned to the middle of reference range. After one year amiodarone was restarted due to deterioration of the arrhythmia, this time permanently. In the time of next 5 years his TSH levels were gradually increasing up to 32 mIU/l, in spite of increasing levothyroxin dose up to 125 μg. FT4 level after initial rise to 27.07 pmol/l was decreasing to high normal values near 22 pmol/l. FT3 concentrations remained close to the lower limit, however recently FT3 concentration fell below normal range to 2.29 pmol/l.
Conclusions: Late onset of AIH in our patient (after 8 years of amiodarone therapy) indicates on a necessity of a life-long monitoring of thyroid function in all patients treated with amiodarone. TSH and FT3 rather than FT4 concentrations should be used to determine levothyroxine dose in AIH patients.
Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.
Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.