Numerous factors have been identified for causing hypothyroidism. The factors are further grouped as causes for primary hypothyroidism and secondary hypothyroidism. Each of the factors is discussed below.
- Hashimoto's Disease
Hashimoto's disease occurs when the immune or protective mechanisms of the body mistakenly attack the thyroid gland. When the immune system attacks the thyroid gland, it damages part of the gland in such a way that it can no longer produce thyroid hormone.
- Iatrogenic hypothyroidism
Iatrogenic hypothyroidism occurs when the thyroid gland has been exposed to large amounts of radiation. The radiation kills certain cells in the thyroid gland that are responsible for producing thyroid hormone. This occurs most often in patients who have received radiation treatment for Graves' disease or neck cancers.
- Consumption of high iodine containing foods and medicines (goitrogens)
Excess consumption of iodized salt, seaweed, cabbage, brussel sprouts, broccoli, cauliflower, mustard, turnips, canola, oil, soy, pine and peanuts. Also, iodides (SSKI, Lugol?s solution), which are often used in combination with surgery to treat hyperthyroidism can cause hypothyroidism if not used properly.
- Iodine deficiency
The thyroid gland requires iodine as one of its building blocks for making thyroid hormone. If there is a lack of iodine in the body, the thyroid gland will not have enough to make the amount of thyroid hormone needed for the body to function properly.
- Enzyme defects
The thyroid gland also requires certain enzymes to make thyroid hormone. Enzymes are proteins that the body uses to help convert one substance into another.
- Thyroid gland removal
Many times, part or all of the thyroid gland will need to be removed if cancer is present in the thyroid gland. With the removal of part or all of the thyroid gland, less thyroid hormone will be produced.
- Medication
Certain medications (such as lithium, interferons, and amiodarone) can have a negative effect on the thyroid gland causing it to produce less thyroid hormone.
- Other diseases
Certain diseases that affect the connective tissues in the body (for example, sarcoidosis, amyloidosis, and scleroderma) can affect the thyroid gland as well. When these diseases reach the thyroid gland, they add tissue (called connective tissue) that is different than thyroid gland tissue, which ends up taking the place of the thyroid gland tissue. The connective tissue that replaces the thyroid gland tissue does not have the ability to produce thyroid hormone.
- Congenital disease
Although it is rare, approximately 1 in 5,000 babies are born with a malfunctioning thyroid gland or no thyroid gland at all.
- Pituitary disease
Pituitary disease can be caused by tumors, surgery, or radiation therapy. Each of these causes a decrease in pituitary gland size and functioning. When the pituitary gland gets smaller as the result of tumors, surgery, or radiation, it cannot produce enough hormone (known as thyroid stimulating hormone--or TSH). TSH tells the thyroid gland to produce thyroid hormone.
- Sheehan's syndrome
Sheehan's syndrome occurs when there is necrosis (cell death) of the pituitary gland. This syndrome is related to severe bleeding during childbirth in women.
- Hypothalamic hypothyroidism
Just as the pituitary gland releases thyroid stimulating hormone (TSH) to tell the thyroid gland to produce thyroid hormone, there is a hormone (called thyrotropin-releasing hormone) released from the hypothalamus, an area in the brain that tells the pituitary gland to release parathyroid hormone. Although it is rare, there is sometimes a problem with the hypothalamus in which thyrotropin-releasing hormone is not released. This can be caused by radiation to the brain, trauma to the head, or other conditions that affect the brain.
What causes it?
