The Treatment of Thyroid Problems with Iodine
There are many aspects of the mechanism controlling the thyroid gland which can cease to function properly. Hyperthyroidism (thyrotoxicosis) and thyroid cancer are the only conditions treated with different forms of iodine.
Hyperthyroidism is where an excess of thyroid hormone is produced causing a high metabolic rate with an increase in temperature and sweating. Also nervousness, tachycardia and weight loss causing an increase in appetite can occur. There are two main types of hyperthyroidism:
1) Diffuse Toxic Goitre (Graves' Disease) - this is caused by an antibody called thyroid stimulating antibody which causes the thyroid cells to grow and produce large quantities of thyroid hormone.
2) Toxic Nodular Goitre - this is where thyroid growth is localised to a particular part of the thyroid gland. This may occur in patients with long-term simple goitre (usually due to a deficiency of dietary iodine eventually causing enlargement of the thyroid but normal thyroid hormone secretion.)
131I is a major line of treatment for hyperthyroidism and thyroid cancer. It is given orally in a single dose and is taken up by the thyroid as if it were the stable isotope of iodine. 131I emits g-rays which pass through the tissue and out of the body and b-particles which destroy the neighbouring cells in the thyroid. Although the half-life of 131I is 8 days and there is virtually none remaining in the body after 2 months, the effect can only be seen after 1-2 months and the toxic effects reach a maximum after 4 months. This treatment will lead to hypothyroidism (where not enough thyroid hormone is being produced). This can be overcome by replacement therapy with thyroxine.
Iodine solution given orally in potassium iodide is converted to the iodide anion in the body. High concentrations of iodide inhibit thyroid hormone production and symptoms subside in 1-2 days. The effect usually peaks after 10-14 days and then decreases. This can be used as a pre-operative treatment since it causes the thyroid to shrink back to its original size and to become firmer. It can also be used as part of a treatment for thyrotoxic crisis.
Rang, Dale, Ritter, Pharmacology, 4th Ed., Churchill Livingstone,1999