Editing Hyperthyroidism (section)

===Radioiodine===
In [[iodine-131]] ([[radioiodine]]) [[Radiation therapy#Radioisotope and therapy (RIT)|radioisotope therapy]], which was first pioneered by Dr. [[Saul Hertz]],<ref name="Vignette">{{cite journal | vauthors = Hertz BE, Schuller KE | title = Saul Hertz, MD (1905-1950): a pioneer in the use of radioactive iodine | journal = Endocrine Practice | volume = 16 | issue = 4 | pages = 713–5 | date = 2010 | pmid = 20350908 | doi = 10.4158/EP10065.CO }}</ref> radioactive iodine-131 is given orally (either by pill or liquid) on a one-time basis, to severely restrict, or altogether destroy the function of a hyperactive thyroid gland. This isotope of radioactive iodine used for ablative treatment is more potent than diagnostic radioiodine (usually [[iodine-123]] or a very low amount of iodine-131), which has a biological half-life from 8–13 hours. Iodine-131, which also emits beta particles that are far more damaging to tissues at short range, has a half-life of approximately 8 days.  People not responding sufficiently to the first dose are sometimes given an additional radioiodine treatment, at a larger dose. Iodine-131 in this treatment is picked up by the active cells in the thyroid and destroys them, rendering the thyroid gland mostly or completely inactive.<ref name="Pmid">{{cite journal | vauthors = Metso S, Auvinen A, Huhtala H, Salmi J, Oksala H, Jaatinen P | title = Increased cancer incidence after radioiodine treatment for hyperthyroidism | journal = Cancer | volume = 109 | issue = 10 | pages = 1972–1979 | date = May 2007 | pmid = 17393376 | doi = 10.1002/cncr.22635 | s2cid = 19734123 | doi-access = free }}</ref>

Since iodine is picked up more readily (though not exclusively) by thyroid cells, and (more important) is picked up even more readily by over-active thyroid cells, the destruction is local, and there are no widespread side effects with this therapy. Radioiodine ablation has been used for over 50 years, and the only major reasons for not using it are pregnancy and breastfeeding ([[Breast|breast tissue]] also picks up and concentrates iodine). Once the thyroid function is reduced, replacement hormone therapy ([[levothyroxine]]) taken orally each day replaces the thyroid hormone that is normally produced by the body.<ref>{{cite web
 | work = AHFS Patient Medication Information
 | publisher = American Society of Health-System Pharmacists, Inc
 | title = levothyroxine
 | url = https://medlineplus.gov/druginfo/meds/a682461.html
 | access-date = 25 October 2021 }}</ref>

There is extensive experience, over many years, of the use of radioiodine in the treatment of thyroid overactivity and this experience does not indicate any increased risk of thyroid cancer following treatment. However, a study from 2007 has reported an increased number of cancer cases after radioiodine treatment for hyperthyroidism.<ref name="Pmid" />

The principal advantage of radioiodine treatment for hyperthyroidism is that it tends to have a much higher success rate than medications. Depending on the dose of radioiodine chosen, and the disease under treatment (Graves' vs. toxic goiter, vs. hot nodule etc.), 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.<ref>{{cite web |url=http://www.mythyroid.com/iodinehyper.html |title=Radioactive Iodine | date = 2005 | work = MyThyroid.com |access-date=2010-05-11 |url-status=dead |archive-url=https://web.archive.org/web/20100305000205/http://www.mythyroid.com/iodinehyper.html |archive-date=5 March 2010 }}</ref>

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 [[thyroid epithelial cell|thyrocytes]] and retro-orbital tissue.<ref>{{cite journal | vauthors = Walsh JP, Dayan CM, Potts MJ | title = Radioiodine and thyroid eye disease | journal = BMJ | volume = 319 | issue = 7202 | pages = 68–69 | date = July 1999 | pmid = 10398607 | pmc = 1116221 | doi = 10.1136/bmj.319.7202.68 }}</ref>

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 blocker]]s ([[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. On occasion, neck tenderness or a sore throat may become apparent after a few days, if moderate inflammation in the thyroid develops and produces discomfort in the neck or throat area. This is usually transient, and not associated with a fever, etc.{{citation needed|date=August 2020}}

It is recommended that breastfeeding be stopped at least six weeks before radioactive iodine treatment and that it not be resumed, although it can be done in future pregnancies. It also shouldn't be done during pregnancy, and pregnancy should be put off until at least 6–12 months after treatment.<ref>{{Cite web |title=Radioactive Iodine Therapy: What is it, Treatment, Side Effects |url=https://my.clevelandclinic.org/health/treatments/16477-radioiodine-radioactive-iodine-therapy |access-date=2022-04-20 |website=Cleveland Clinic}}</ref><ref>{{Cite web |title=Radioactive Iodine |url=https://www.thyroid.org/radioactive-iodine/ |access-date=2022-04-20 |website=American Thyroid Association |language=en-US}}</ref>

A common outcome following radioiodine is a swing from hyperthyroidism to the easily treatable hypothyroidism, which occurs in 78% of those treated for Graves' thyrotoxicosis and in 40% of those with toxic multinodular goiter or solitary toxic adenoma.<ref name=pmid1710255>{{cite journal | vauthors = Berglund J, Christensen SB, Dymling JF, Hallengren B | title = The incidence of recurrence and hypothyroidism following treatment with antithyroid drugs, surgery or radioiodine in all patients with thyrotoxicosis in Malmö during the period 1970-1974 | journal = Journal of Internal Medicine | volume = 229 | issue = 5 | pages = 435–442 | date = May 1991 | pmid = 1710255 | doi = 10.1111/j.1365-2796.1991.tb00371.x | s2cid = 10510932 }}</ref> Use of higher doses of radioiodine reduces the number of cases of treatment failure, with penalty for higher response to treatment consisting mostly of higher rates of eventual hypothyroidism which requires hormone treatment for life.<ref name=pmid16390021>{{cite journal | vauthors = Esfahani AF, Kakhki VR, Fallahi B, Eftekhari M, Beiki D, Saghari M, Takavar A | title = Comparative evaluation of two fixed doses of 185 and 370 MBq 131I, for the treatment of Graves' disease resistant to antithyroid drugs | journal = Hellenic Journal of Nuclear Medicine | volume = 8 | issue = 3 | pages = 158–161 | year = 2005 | pmid = 16390021 }}</ref>

There is increased sensitivity to radioiodine therapy in thyroids appearing on [[Medical ultrasonography|ultrasound scans]] as more uniform (hypoechogenic), due to densely packed large cells, with 81% later becoming hypothyroid, compared to just 37% in those with more normal scan appearances (normoechogenic).<ref name=pmid17609305>{{cite journal | vauthors = Markovic V, Eterovic D | title = Thyroid echogenicity predicts outcome of radioiodine therapy in patients with Graves' disease | journal = The Journal of Clinical Endocrinology and Metabolism | volume = 92 | issue = 9 | pages = 3547–3552 | date = September 2007 | pmid = 17609305 | doi = 10.1210/jc.2007-0879 | doi-access = free }}</ref>