SUN-408 - A Transient Rise and Fall: Wolff-Chaikoff Effect Following Supratherapeutic Amiodarone Exposure

An 82-year-old female with peripheral arterial disease, coronary artery disease, and atrial fibrillation status post Watchman device, lung cancer in remission, presented with abdominal pain and nausea. She had been recently hospitalised for atrial fibrillation with rapid ventricular response and was discharged one week back on amiodarone 400 mg twice daily. Thyroid function testing prior to amiodarone initiation demonstrated a normal thyroid-stimulating hormone (TSH) of 2.08 µIU/mL. The patient unintentionally ingested 1200 mg daily for approximately one week. On presentation one week later, she was hypotensive and bradycardic, requiring vasopressor support and intravenous fluids. Laboratory evaluation revealed TSH of 9.90 µIU/mL with normal free T4 of 1.07 ng/dL and free T3 of 2.11 pg/mL. Repeat thyroid testing three days later demonstrated normalization of TSH to 0.89 µIU/mL, with a stable free T4 of 0.97 ng/dL and a decline in free T3 to 1.17 pg/mL. The patient denied prior thyroid disease or symptoms of hypothyroidism. This transient TSH elevation, accompanied by a reduction in T3 in the setting of acute iodine excess attributed to amiodarone exposure, is consistent with the Wolff-Chaikoff effect and impaired peripheral T4 to T3 conversion. The biochemical improvement and lack of clinical hypothyroidism supported the decision to initiate no thyroid-specific therapy. Amiodarone dosing was corrected, cardiac function was optimised, and outpatient thyroid function monitoring was planned.

Conclusion:
This case illustrates acute, reversible iodine-induced thyroid dysfunction due to supratherapeutic amiodarone exposure, and rapid biochemical changes consistent with the Wolff-Chaikoff phenomenon. Recognition of early thyroid changes and appropriate conservative management can prevent unnecessary treatment in asymptomatic patients.

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