Hypothyroidism - Causes

Causes

Iodine deficiency is the most common cause of hypothyroidism worldwide. In iodine-replete individuals hypothyroidism is frequently caused by Hashimoto's thyroiditis, or otherwise as a result of either an absent thyroid gland or a deficiency in stimulating hormones from the hypothalamus or pituitary.

Factors such as iodine deficiency or exposure to iodine-131 from nuclear fallout, which is absorbed by the thyroid gland like regular iodide and destroys its cells, can increase the risk.

Congenital hypothyroidism is very rare accounting for approximately 0.2% and can have several causes such as thyroid aplasia or defects in the hormone metabolism. Thyroid hormone insensitivity (most often T3 receptor defect) also falls into this category although in this condition the levels of thyroid hormones may be normal or even markedly elevated.

Hypothyroidism can result from postpartum thyroiditis, a condition that affects about 5% of all women within a year of giving birth. The first phase is typically hyperthyroidism; the thyroid then either returns to normal, or a woman develops hypothyroidism. Of those women who experience hypothyroidism associated with postpartum thyroiditis, one in five will develop permanent hypothyroidism requiring lifelong treatment.

Hypothyroidism can result from de Quervain's thyroiditis, which, in turn, is often caused by having a bad flu that enters and destroys part, or all, the thyroid.

Hypothyroidism can also result from sporadic inheritance, sometimes autosomal recessive.

Temporary hypothyroidism can be due to the Wolff-Chaikoff effect. A very high intake of iodine can be used to temporarily treat hyperthyroidism, especially in an emergency situation. Although iodide is a substrate for thyroid hormones, high levels reduce iodide organification in the thyroid gland, decreasing hormone production. The antiarrhythmic agent amiodarone can cause hyper- or hypothyroidism due to its high iodine content.

Hypothyroidism can be caused by lithium-based mood stabilizers, usually used to treat bipolar disorder (previously known as manic depression). In fact, lithium has occasionally been used to treat hyperthyroidism. Other drugs that may produce hypothyroidism include interferon alpha, interleukin-2, and thalidomide.