Amiodarone-Induced Thyroid Dysfunction: Causes, Symptoms, Diagnosis, and Treatment
What is Amiodarone-Induced Thyroid Dysfunction?
Amiodarone-Induced Thyroid Dysfunction (AITD) refers to thyroid disorders caused by amiodarone, a medication used to treat irregular heartbeats (arrhythmias). Amiodarone contains a high iodine content, which can affect thyroid function, leading to either hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid).
What Are the Symptoms of Amiodarone-Induced Thyroid Dysfunction?
The symptoms depend on whether the condition leads to hypothyroidism or hyperthyroidism.
Symptoms of Amiodarone-Induced Hypothyroidism (AIH)?
- Fatigue and weakness
- Weight gain
- Dry skin and hair loss
- Cold intolerance
- Depression and mood changes
- Slow heart rate (bradycardia)
- Constipation
Symptoms of Amiodarone-Induced Hyperthyroidism (AIT)?
- Unexplained weight loss
- Rapid or irregular heartbeat (palpitations)
- Excessive sweating and heat intolerance
- Tremors (shaking hands)
- Anxiety and restlessness
- Muscle weakness
- Increased bowel movements
What Causes Amiodarone-Induced Thyroid Dysfunction?
The condition results from the effects of amiodarone on thyroid hormone production. Amiodarone contains 37% iodine by weight, and taking the drug provides massive amounts of iodine, which can disrupt normal thyroid function.
Types of Amiodarone-Induced Thyroid Dysfunction?
- Amiodarone-Induced Hypothyroidism (AIH)?
- Occurs when excess iodine suppresses thyroid hormone production (Wolff-Chaikoff effect).
- More common in people with pre-existing thyroid conditions, such as Hashimoto’s thyroiditis.
- Amiodarone-Induced Hyperthyroidism (AIT)?
- Occurs when excess iodine triggers excessive thyroid hormone production.
- More common in people with nodular goiter or latent Graves’ disease.
- Two subtypes:
- Type 1 AIT – Increased thyroid hormone production due to iodine excess.
- Type 2 AIT – Inflammation of the thyroid gland (thyroiditis) causing hormone leakage.
How is Amiodarone-Induced Thyroid Dysfunction Diagnosed?
1. Blood Tests?
- TSH (Thyroid-Stimulating Hormone) – Low in hyperthyroidism, high in hypothyroidism.
- Free T3 and T4 – Elevated in hyperthyroidism, low in hypothyroidism.
- Thyroid autoantibodies – Used to check for autoimmune thyroid diseases (Graves’ or Hashimoto’s).
2. Thyroid Ultrasound?
- Helps differentiate between Type 1 and Type 2 AIT.
- Detects nodules, goiter, or inflammation.
3. Radioactive Iodine Uptake (RAIU) Scan?
- Low uptake suggests Type 2 AIT (thyroiditis).
- Normal or high uptake suggests Type 1 AIT (iodine-induced hyperthyroidism).
What Are the Treatment Options for Amiodarone-Induced Thyroid Dysfunction?
For Amiodarone-Induced Hypothyroidism (AIH)?
- Levothyroxine (Synthroid) to replace thyroid hormones.
- Regular monitoring of TSH levels.
- Amiodarone may or may not need to be stopped, depending on the severity.
For Amiodarone-Induced Hyperthyroidism (AIT)?
- Type 1 AIT Treatment?
- Antithyroid drugs (Methimazole or Propylthiouracil) to reduce thyroid hormone production.
- Beta-blockers (Propranolol, Atenolol) to control heart rate and symptoms.
- Potassium perchlorate to reduce iodine absorption (in some cases).
- Type 2 AIT Treatment?
- Glucocorticoids (Prednisone) to reduce thyroid inflammation.
- Beta-blockers for symptom relief.
- Stopping amiodarone may be necessary in severe cases.
- Severe Cases?
- Thyroidectomy (surgical removal of the thyroid) if other treatments fail.
- Radioactive iodine therapy in some cases.
Can Amiodarone-Induced Thyroid Dysfunction Be Prevented?
- Regular thyroid function tests before and during amiodarone treatment.
- Monitoring iodine intake to avoid excessive levels.
- Early intervention if thyroid dysfunction symptoms appear.