How amiodarone affects the thyroid gland?
What thyroid-related diseases may occur due to prolonged treatment with amiodarone?
1 in 6 patients taking amiodarone develop thyroid dysfunction.
Half life of amiodarone is very long 100 days that result in prolong effects even after stopping therapy.Amiodarone can cause hypothyroidism and hyperthyroidism.
Amiodarone induced Hypothyroidism
Pathophysiology of AIH is due to high iodine content of amiodarone causing wolff- chaikoff effect(it is an autoregulatory phenomenon where thyroxine formation is inhibited due to high levels of circulating iodine.Iodine driven inhibition if thyroid hormone sythesis).TSH will be high T3 low with normal or elevated T4 as amiodarone inhibit peripheral conversion of T4 to T3.
*Amiodarone may be continued if this is desirable, in that case thyroxine is added along with Amiodarone.
Amiodarone induced Thyrotoxicosis
AIT is further subdivided in to 2 types.
AIT type 1:
*It is due to accelerated hormone synthesis secondary to iodide load(Jod-Basedow effect)
*Occur in patients with underlying latent thyroid pathophysiology.
*There will be increased flow on duplex US on thyroid for blood flow.
*Normal or high iodine uptake in iodide 131 scan.
*Management include Antithyroid drugs like carbimazole.
*Amiodarone must be stopped in patient who develop AIT.
AIT type 2:
Amiodarone related destructive thyroiditis with direct effect of amiodarone in follicular cells with breakdown of cells and release of preformed thyroid hormones.This is direct toxic effect on follicular cells with out underlying thyroid disease.Clinically neck tenderness is feature.
*Ultrasound duplex show decreased blood flow.
*Low or none uptake in iodine 131 uptake scan
*Management include steroids.