An overactive thyroid, a condition known as hyperthyroidism, occurs when the thyroid gland located in the neck produces too much of the hormones thyroxine (T4) and triiodothyronine (T3). Hyperthyroidism can be an acute (short-term) or chronic (long-term) condition resulting in symptoms such as difficulty concentrating, fatigue, frequent bowel movement, increased appetite, sweating, restlessness and change in weight. There are several different diseases or conditions that cause an overactive thyroid, which occurs in approximately 1 percent of the United States population, according to the National Endocrine and Metabolic Diseases Information Service.
Graves' Disease
Graves' disease is an autoimmune disorder, meaning that the body's own immune system attacks the healthy cells and tissues in itself. In patients with Graves' disease the immune system produces antibodies, called thyroid-stimulating immunoglobulin (TSI), against the thyroid cells. These antibodies mimic the actions of thyroid stimulating hormone (TSH), a hormone produced by the pituitary gland that triggers the production of the thyroid hormones. As a result the thyroid produces increased levels of both T3 and T4 thyroid hormones.
Noncancerous Growths
Glands, such as the thyroid gland or pituitary gland, can form noncancerous lumps when areas of the gland wall itself off from the rest of the gland. These lumps are called adenomas.
A pituitary adenoma can cause an overproduction of TSH, which then triggers the thyroid to produce too much thyroid hormone. Thyroid adenoma, occurring in approximately 3 to 7 percent of the population as reported by the National Endocrine and Metabolic Diseases Information Service, can cause the thyroid to become overactive and produce too much thyroid hormone.
A toxic adenoma is the term for an overactive thyroid adenoma. When more than one adenoma is present causing the overactive thyroid, the condition is known as toxic multinodular goiter.
Thyroiditis
Thyroiditis is inflammation of the thyroid gland that results in stored thyroid hormone leaking from the gland, raising the levels of hormone in the bloodstream. The most common type of thyroiditis is silent thyroiditis, called silent because it is painless, which may result in a permanent overactive thyroid.
Subacute thyroiditis, which may be caused by a bacterial or viral infection, is a painful condition but usually resolves on its own within a few months. But it can cause permanent overactive thyroid according to the National Institutes of Health.
Postpartum thyroiditis affects approximately 8 percent of women after giving birth, according to the National Endocrine and Metabolic Diseases Information Service. The thyroid may remain overactive for 1 to 2 months and the condition will usually occur following subsequent pregnancies.
