amiodarone-induced thyrotoxicosis

Amiodarone Induced Thyrotoxicosis (AIT) can occur can occur any time a patient is on amiodarone with average of about 3 years before a diagnosis is made.


There are two key terms that always come up when talking about amiodarone-induced thyroiditis.

(1) Wolff-Chaikoff effect - this is the hypothesis that excess iodine will cause hypothyroidism. Amiodarone is almost 40% iodine. There usually is mention of "escape from the Wolff-Chaikoff effect" where the thyroid function returns to normal which usually happens after about 10 days.
(2) Job-Basedow effect - hyperthyroidism that occurs after the adminstration of iodine such as via amiodarone or contrast which provide more substrate for making thyroid hormone.

There are also two types of amiodarone induces thyroiditis:
Type I - is attributed to excess iodine prividing extra substate and leading to inceased production of thyroid hormone. It is usually seen in patients who have an underlying thyroid problem such as Grave's or multinodular goiter. Color flow doppler shows increased flow. Serum IL-6 levels are normal or slighly elevated.
Type II - is from a destructive process attributed to the toxic effects of amiodarone. Color flow doppler shows decreased flow. Serum IL-6 levels are hypothesized to be an indicator of thyroid destructive processes and are markedly elevated. The increased thyroid function is secondary to leakage of hormones as cells are destroyed.

Type I is usually treated with thioamindes like methiazole 30-40 mg daily along with potassium perchlorate 1g/day for 16-40 days). Amiodarone should be discontinuted. After the thyroid and normalization of iodine in the urine, the patient should be treated with radiation or thyroidectomy.

Type II can be treated with glucocorticoids for up to 2-3 months (start prednisone 40mg/day). Stop amio. Can add thioamide and potassium perchlorate. When pt becomes euthyroid, cont to monitor for hypothyroidism.