), the success rate in achieving definitive resolution of the hyperthyroidism may vary from 75 to 100%. A major expected side-effect of radioiodine in people with Graves disease is the development of lifelong hypothyroidism, requiring daily treatment with thyroid hormone. On occasion, some people may require more than one radioactive treatment, depending on the type of disease present, the size of the thyroid, and the initial dose administered.People with Graves disease manifesting moderate or severe Graves ophthalmopathy are cautioned against radioactive iodine-131 treatment, since it has been shown to exacerbate existing thyroid eye disease. People with mild or no ophthalmic symptoms can mitigate their risk with a concurrent six-week course of prednisone. The mechanisms proposed for this side effect involve a TSH receptor common to both thyrocytes and retro-orbital tissue.As radioactive iodine treatment results in the destruction of thyroid tissue, there is often a transient period of several days to weeks when the symptoms of hyperthyroidism may actually worsen following radioactive iodine therapy. In general, this happens as a result of thyroid hormones being released into the blood following the radioactive iodine-mediated destruction of thyroid cells that contain thyroid hormone. In some people, treatment with medications such as beta blockers (propranolol, atenolol, etc.) may be useful during this period of time. Most people do not experience any difficulty after the radioactive iodine treatment, usually given as a small pill.
There is also an increased risk of bone fractures (by 42%) in people with subclinical hyperthyroidism; there is insufficient evidence to say whether treatment with antithyroid medications would reduce that risk.A 2022 meta-analysis found subclinical hyperthyroidism to be associated with cardiovascular death. Screening
In those without symptoms who are not pregnant there is little evidence for or against screening. Treatment
Antithyroid drugs
Thyrostatics (antithyroid drugs) are drugs that inhibit the production of thyroid hormones, such as carbimazole (used in the UK) and methimazole (used in the US, Germany and Russia), and propylthiouracil. Thyrostatics are believed to work by inhibiting the iodination of thyroglobulin by thyroperoxidase and, thus, the formation of tetraiodothyronine (T4). Propylthiouracil also works outside the thyroid gland, preventing the conversion of (mostly inactive) T4 to the active form T3. Because thyroid tissue usually contains a substantial reserve of thyroid hormone, thyrostatics can take weeks to become effective and the dose often needs to be carefully titrated over a period of months, with regular doctor visits and blood tests to monitor results.A very high dose is often needed early in treatment, but, if too high a dose is used persistently, people can develop symptoms of hypothyroidism. This titrating of the dose is difficult to do accurately, and so sometimes a "block and replace" attitude is taken. In block and replace treatments thyrostatics are taken in sufficient quantities to completely block thyroid hormones, and the person treated as though they have complete hypothyroidism.