OVERVIEW

What is iodine-induced hyperthyroidism?

Iodine is the raw material for the thyroid to synthesize thyroid hormones. If a large amount of iodine-rich food or medication enters the body, causing the thyroid to synthesize and secrete excessive thyroid hormones, it can lead to hyperthyroidism, resulting in increased excitability of the nervous, circulatory, and digestive systems, as well as hypermetabolism. This condition is called iodine-induced hyperthyroidism, or iodine-induced thyrotoxicosis for short.

How common is iodine-induced hyperthyroidism?

Studies show that after iodine supplementation in iodine-deficient areas, the prevalence of this disease is approximately 1% to 20%.

Who is more likely to develop iodine-induced hyperthyroidism?

This condition can occur in anyone. However, individuals with pre-existing thyroid diseases, such as toxic thyroid adenoma or toxic multinodular goiter, are more susceptible to developing it.

In healthy individuals, thyroid follicular cells have a certain self-regulatory mechanism for iodine intake, which helps avoid fluctuations in thyroid function. However, patients with pre-existing thyroid disorders often have defects in this self-regulatory function, making them more prone to the disease.

SYMPTOMS

What are the common manifestations of iodine-induced hyperthyroidism?

Hyperthyroidism can involve multiple organ systems, including:

• Skin: Excessive sweating, warm and smooth skin, itching, brittle nails, onycholysis, thinning hair, etc.;

• Cardiovascular system: Palpitations, increased heart rate, elevated blood pressure, atrial fibrillation, or even heart failure;

• Endocrine and metabolism: Decreased blood lipids, weight loss, elevated blood sugar;

• Respiratory system: Dyspnea, especially after activity;

• Digestive system: Increased bowel movements, abnormal liver function, vomiting, abdominal pain, or jaundice in some patients;

• Hematologic system: Anemia, decreased white blood cells and platelets;

• Genitourinary system: Frequent urination, nocturia; in women—prolonged menstrual cycles, anovulation, amenorrhea; in men—gynecomastia, decreased libido, erectile dysfunction, reduced sperm count;

• Bones: Osteoporosis, fractures, clubbing of fingers or toes in some patients;

• Neurological and psychiatric systems: Hand tremors, anxiety, irritability, mood instability; elderly patients may exhibit apathy, while children may have poor concentration and declining academic performance.

Can iodine-induced hyperthyroidism lead to serious consequences?

Severe cases may result in heart failure or even sudden death. Critical patients can develop thyroid storm, which is life-threatening.

CAUSES

What causes iodine-induced hyperthyroidism?

The main cause of this condition is excessive iodine intake, leading to the overproduction of thyroid hormones. Sources of excess iodine include:

• Oral or topical iodine-containing medications for skin or vaginal mucosa;

• Use of contrast agents for angiography or CT scans;

• Excessive consumption of iodine-rich foods such as seaweed or kelp.

DIAGNOSIS

What tests are needed for iodine-induced hyperthyroidism?

• Thyroid function: Used to diagnose whether hyperthyroidism exists and its severity.

• Thyrotropin receptor antibody (TRAb): Used to differentiate whether hyperthyroidism is caused by Graves' disease. A positive result usually indicates Graves' disease.

• Thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb): Used to assist in diagnosing whether other thyroid diseases are present, such as transient thyrotoxicosis caused by Hashimoto's thyroiditis.

• Thyroid ultrasound or radionuclide imaging: Used to help determine whether the cause of hyperthyroidism is excessive iodine intake.

• 24-hour urinary iodine: Used to assist in diagnosing iodine-induced hyperthyroidism. If hyperthyroidism is diagnosed along with decreased radionuclide uptake on thyroid imaging and 24-hour urinary iodine exceeding 1,000 µg, iodine-induced hyperthyroidism is highly likely.

What diseases is iodine-induced hyperthyroidism easily confused with?

This condition is easily confused with hyperthyroidism caused by toxic thyroid adenoma, pituitary thyrotropinoma, or Graves' disease, as well as transient thyrotoxicosis caused by autoimmune thyroiditis (e.g., Hashimoto's thyroiditis). The aforementioned common manifestations and related tests can help differentiate these conditions.

TREATMENT

Which department should I visit for iodine-induced hyperthyroidism?

Endocrinology, Thyroid Surgery, or Breast and Thyroid Surgery.

How is iodine-induced hyperthyroidism treated?

Treatment for this condition includes:

• Discontinuing iodine-containing medications and foods.

• Using beta-blockers, such as propranolol or atenolol, to control symptoms like palpitations and tremors.

• For severe hyperthyroidism symptoms, a duration of >1 month, or elderly patients with heart disease, antithyroid medications like methimazole or propylthiouracil may be prescribed.

• If Graves' disease is present, long-term antithyroid drug therapy, radioactive ¹³¹I treatment, or surgery may be considered.

• For toxic thyroid adenoma or toxic multinodular goiter, radioactive ¹³¹I treatment or surgery is often preferred.

How long should antithyroid drugs be used for iodine-induced hyperthyroidism?

For Graves' disease, the treatment course typically lasts 1.5–2 years, sometimes longer. For toxic thyroid adenoma or toxic multinodular goiter, antithyroid drugs can be gradually reduced and discontinued within 6–12 months.

Do antithyroid drugs for iodine-induced hyperthyroidism have significant side effects?

Side effects include:

• Allergic skin reactions: May cause itching, rashes, or exfoliative dermatitis.

• Neutropenia or agranulocytosis: May lead to fatigue, fever, sore throat, and in severe cases, life-threatening conditions.

• Liver damage: May cause right upper abdominal pain, fatigue, poor appetite, nausea, vomiting, and in severe cases, itching and jaundice.

• Vasculitis: May result in fever, muscle/joint pain, cough, bloody sputum, respiratory failure, proteinuria, hematuria, anemia, and other lung/kidney damage.

Side effects are generally mild, with severe cases being rare. Symptoms may improve or resolve with symptomatic treatment or dose reduction.

What should be noted for radioactive ¹³¹I treatment of iodine-induced hyperthyroidism?

Before treatment: Discontinue methimazole for 3 days or propylthiouracil for ≥2 weeks, stop iodine-containing vitamins for 7–10 days, avoid iodine-rich foods and medications for 2–3 weeks, and discontinue amiodarone for 3–6 months.
After treatment: Since ¹³¹I is radioactive:

• Drink plenty of water and urinate frequently for the first 2 days.

• Stay at home for the first week, maintain a distance of >1.8 meters from others, and avoid sharing utensils.

• Limit close contact with family, especially children and pregnant women, for 1 month.

• Use a separate bathroom if possible, and flush multiple times after use to minimize contamination.

• Avoid pregnancy for 6 months post-treatment.

Is follow-up needed after treatment for iodine-induced hyperthyroidism? How?

Yes.

• For antithyroid drugs: Monitor thyroid function every 4–6 weeks, along with liver function and blood tests, until stable. Afterwards, check thyroid function every 3 months.

• For radioactive ¹³¹I: Monitor thyroid function every 4–6 weeks for 6 months. If remission is confirmed, extend intervals to at least once yearly.

• For surgery: Check thyroid function every 4–6 weeks post-surgery. If thyroid hormone replacement is needed, monitor every 6–8 weeks until stable, then adjust frequency.

Can iodine-induced hyperthyroidism be cured?

If not complicated by Graves' disease, toxic adenoma, or toxic multinodular goiter, thyroid function may normalize after iodine restriction.

If these conditions are present, antithyroid drugs may only relieve symptoms with possible relapse, while radioactive ¹³¹I or surgery can provide a cure.

DIET & LIFESTYLE

What should patients with iodine-induced hyperthyroidism pay attention to in their daily lives?

• Maintain a comprehensive and balanced diet, with appropriate intake of foods rich in protein and vitamins.

• Unless pregnant or breastfeeding, an iodine-restricted diet is recommended.

• Avoid alcohol, tea, and coffee consumption.

• Quit smoking.

• Ensure adequate sleep and maintain an optimistic, relaxed mood.

Can patients with iodine-induced hyperthyroidism have children normally?

It is best for patients with this condition to conceive only after symptom relief, normalization of thyroid function, or complete recovery. Female patients taking antithyroid medications who urgently wish to become pregnant should switch to propylthiouracil.

Is iodine-induced hyperthyroidism hereditary?

This condition is not hereditary.

PREVENTION

Can iodine-induced hyperthyroidism be prevented?

Yes.

Before using iodine-containing medications, check thyroid function and perform ultrasounds. If there is a risk of triggering this condition, avoid using relevant iodine-containing drugs.

After taking iodine-containing medications, follow medical advice to monitor thyroid function for early detection of abnormalities and timely diagnosis/treatment.
Additionally, iodine-rich foods like kelp and seaweed should be consumed in moderation.