Hashimoto’s Thyroiditis: This is the most common cause of hypothyroidism and is categorized as an inherited condition.
Hashimoto’s results from an underlying autoimmune disease, in which the body’s immune system attacks thyroid tissues. This condition usually presents with an enlarged thyroid gland, or goiter, and inhibits the production of thyroid hormones.
Lymphocytic Thyroiditis: Thyroiditis is an inflammation of the thyroid gland. It is thought to be caused by a type of white blood cell known as a lympocyte.
Severe Iodine Deficiency Hypothyroidism: This results from a dietary deficiency of iodine. Severe hypothyroidism resulting from iodine deficiencies are primarily seen in underdeveloped countries.
Hypothyroidism caused by iodine deficiency is so prevalent, in fact, that an estimated 5-15% of the entire population in lesser developed countries (e.g. Chile and India) suffer from this condition.This condition is extremely rare in the U.S., due to the inclusion of iodine in table salt and bread products.
Pituitary or Hypothalamic disease: Pituitary disease is also referred to as “secondary hypothyroidism. “Hypothalamic disease is defined as “tertiary hypothyroidism.” These two conditions result from the inability of either the pituitary gland or hypothalamus to signal the thyroid for hormone production. Even if the thyroid gland itself is normal, a decreased level of circulating T3 or T4 may still occur as a result of these underlying diseases.
Medications: Common medications used to treat hyperthyroidism (over-active thyroid) can actually cause hypothyroidism. Psychiatric medications, like lithium, may also diminish thyroid hormone production. The administration of other drugs that contain large amounts of iodine can also lead to extremely low levels of thyroid hormone within the blood.
Destruction of the Thyroid: Thyroid destruction typically results from radioactive iodine treatments, radiation therapy, or surgical procedure. For instance, Grave’s disease patients (caused by hyperthyroidism) may receive radioactive iodine therapy, resulting in the destruction or impairment of some, or even all of existing thyroid tissue. Removal of the thyroid gland during surgery is also accompanied with hypothyroidism.