Wolff–Chaikoff effect in amiodarone-treated atrial fibrillation

Case Presentation: A 50-year-old man with a history of paroxysmal atrial fibrillation was referred for
assessment of progressive fatigue and unintended weight gain. He had been treated with amiodarone at
a maintenance dose of 200 mg daily for six months for rhythm control, resulting in effective rhythm
control. There was no prior documented history of thyroid disease and baseline thyroid function tests had
not been obtained prior to initiation of amiodarone therapy.
Biochemical evaluation revealed a markedly elevated thyroid-stimulating hormone level (TSH 40 mIU/L)
with reduced free thyroxine concentrations, consistent with overt hypothyroidism. Thyroid autoantibody
testing was positive, suggesting underlying autoimmune thyroid disease. Thyroid ultrasonography
demonstrated glandular enlargement with a macronodular pattern. Collectively, these findings supported
the diagnosis of amiodarone-induced hypothyroidism, most likely resulting from iodine-induced inhibition
of thyroid hormone synthesis due to failure to escape the Wolff–Chaikoff effect in the predisposed thyroid
gland. Following multidisciplinary evaluation, amiodarone therapy was discontinued and levothyroxine
replacement was initiated. The patient experienced progressive symptomatic improvement, accompanied
by normalization of thyroid function tests over a six-month follow-up period. Cardiac rhythm remained
stable and no recurrence of atrial fibrillation was documented.
Amiodarone-induced hypothyroidism represents a frequent and clinically relevant adverse effect,
particularly in patients with underlying thyroid autoimmunity. Management requires individualized
decision-making, balancing the need for effective arrhythmia control against endocrine complications.
This case emphasizes the importance of baseline thyroid evaluation and regular monitoring during
amiodarone therapy. Early recognition and appropriate management of thyroid dysfunction are essential
to optimize both cardiovascular and endocrine outcomes in patients with atrial fibrillation.
Keywords:
Amiodarone; Atrial fibrillation; Hypothyroidism; Wolff–Chaikoff effect; Thyroid dysfunction