Thyroid disease is caused by the overproduction or underproduction of the thyroid hormones, according to WebMD. Overproduction is known as hyperthyroidism, while underproduction is known as hypothyroidism. Both types of thyroid disease are caused by a lack of proper thyroid hormone production regulation, resulting in a severe hormone imbalance.
The most common forms of thyroid disease are caused by a disruption in the immune system, which results in confused antibodies that target the thyroid gland, About.com explains. Hashimoto's thyroiditis is a serious autoimmune disorder that renders the thyroid gland incapable of producing the crucial thyroid hormone.
Hyperthyroidism takes several forms, including Graves' disease, toxic adenomas and subacute thyroiditis, WebMD explains. In each case, the thyroid disease is caused by an excess secretion of the thyroid hormones, altering the body's normal hormone balance.
Hypothyroidism can be induced by a drug or surgical procedure, but also may be due to Hashimoto's thyroiditism, a pituitary disorder, a defective thyroid or lack of the thyroid gland, says WebMD. Hypothyroid diseases always form when the body's production of thyroid hormones is thwarted and the body is unable to maintain normal levels of energy. Although uncommon if treatment is sought in time, hypothyroid diseases can result in a coma and can even be fatal if left untreated, according to About.com.