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Radioiodine therapy for hyperthyroidism
I-131 is trapped by active thyroid cells and irradiates them with short-range beta particles, so it is a simple definitive treatment for Graves disease, toxic adenoma and toxic multinodular goitre — at the price of permanent hypothyroidism in most Graves patients.
Why it matters in the exam
The exam asks about indications and contraindications: pregnancy and breastfeeding are absolute contraindications; active moderate-to-severe ophthalmopathy is a reason to prefer surgery or drugs, and in mild active ophthalmopathy or in smokers prophylactic prednisone is given; a nodule suspicious for malignancy or a large compressive goitre favours surgery. A woman who wants to conceive must wait at least 6 months after treatment, and a man is asked to wait at least 3 months.
Before treatment, antithyroid drugs are stopped 3–5 days earlier so they do not block iodine uptake, and every woman of childbearing age has a pregnancy test. An older patient or one with heart disease first receives methimazole to lower hormone levels, and a beta-blocker is kept throughout. The activity is set by gland size and uptake, or given as a fixed activity (about 370–555 MBq in Graves disease); hot nodules need a higher activity because the tissue is less sensitive.
After treatment: the response begins within 4–8 weeks and the full effect arrives within 3–6 months; free T4 and T3 are checked every 4–6 weeks, because TSH stays suppressed for months. In Graves disease most patients will reach hypothyroidism and that is the goal of treatment, not a complication. In a toxic adenoma the suppressed tissue is protected, so hypothyroidism is less common. Early side effects: a transient worsening of thyrotoxicosis and radiation thyroiditis with neck tenderness. There is no proven increase in cancer or offspring defects at the therapeutic activities used for benign disease. Radiation advice for home: distance from children and pregnant women for several days, a separate toilet and double flushing.
Key points
- I-131 is definitive treatment for Graves disease and toxic nodules.
- Pregnancy and breastfeeding are contraindications; wait at least 6 months before pregnancy.
- Active moderate-to-severe ophthalmopathy — not I-131; mild — prophylactic prednisone.
- Stop antithyroid drugs 3–5 days before treatment.
- Follow free T4 and T3 every 4–6 weeks; hypothyroidism is expected in Graves.
Summary table
| Situation | Suitability for I-131 | Note |
|---|---|---|
| Graves disease without ophthalmopathy | Very suitable | Hypothyroidism expected and accepted |
| Graves with mild active ophthalmopathy or a smoker | Suitable with prophylactic prednisone | Encourage smoking cessation |
| Graves with active moderate-to-severe ophthalmopathy | Not preferred | Drugs or surgery |
| Toxic adenoma or multinodular goitre | Suitable | Higher activity; hypothyroidism less common |
| Pregnancy, breastfeeding, pregnancy planned within half a year | Contraindicated | Drugs or surgery |
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Sources
- American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis, 2016 — Radioactive iodine therapy for Graves disease and toxic nodular goitre
- EANM Procedure Guidelines for Therapy of Benign Thyroid Disease, 2010 — Patient preparation, activity and follow-up
- European Thyroid Association Guideline for the Management of Graves Hyperthyroidism, 2018 — Radioiodine and Graves orbitopathy
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.