May 21, 2012
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May 21, 2012
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Overview
The thyroid is a small gland that is located in the front of the neck below the larynx, or voice box. Along with the pituitary, adrenal, and other glands, the thyroid is part of the endocrine system, which produces, stores, and releases hormones into the blood stream to control various functions of the body’s cells. The production of thyroid hormones is regulated by thyroid-stimulating hormone (TSH), which is made by the pituitary gland. The thyroid hormones are known as triiodothyronine (T3) and thyroxine (T4).
What Is the Function of the Thyroid?
The thyroid produces hormones that regulate the body’s metabolism—the way the body uses energy. In addition to their effects on metabolism, thyroid hormones also affect brain development, breathing, heart and nervous system functions, body temperature, muscles strength, skin dryness, menstrual cycles, weight, and cholesterol levels.
Thyroid Imbalances
Hyperthyroidism
Hyperthyroidism is a disorder that occurs when the thyroid makes more thyroid hormone than the body needs. According to the National Institutes of Health (NIH), hyperthyroidism affects about 1 percent of the U.S. population and women are five to 10 times more likely to develop the disorder than men.
Factors that may increase chances of developing hyperthyroidism include a personal or family history of thyroid problems, certain medical conditions (pernicious anemia, type 1 diabetes, or adrenal insufficiency), a diet high in iodine, use of iodine-containing medications, age older than 60 years, and pregnancy or birth within the past six months.
Causes of hyperthyroidism include:
Symptoms of hyperthyroidism include:
Diagnosing Hyperthyroidism
To diagnose hyperthyroidism, a doctor will discuss a patient’s symptoms and perform a physical examination. If he or she finds reason to suspect hyperthyroidism, several tests may be used to confirm a diagnosis. Tests are also used to help determine the cause of the condition.
Tests for diagnosing hyperthyroidism include:
Thyroid-stimulating Hormone (TSH) Test
This test detects small amounts of TSH in the blood to measure thyroid activity. When there is too much thyroid hormone in the blood, the pituitary gland stops producing TSH. In general, a TSH level reading below normal indicates hyperthyroidism and a reading above normal indicates hypothyroidism.
T3 and T4 Test
If you have hyperthyroidism, this test will show that levels of T3 and/or T4 are higher than normal.
Radioactive Iodine Uptake Test
A measurement of the amount of iodine your thyroid collects from the bloodstream, this test will help show what is causing hyperthyroidism. Different levels of iodine uptake indicate different conditions.
Thyroid Scan
This scan shows how and where iodine is distributed in your thyroid to help diagnose the cause of hyperthyroidism.
Treating Hyperthyroidism
Doctors consider the cause of hyperthyroidism and how severe it is when choosing treatment. Other factors like a patient’s age, possible allergies to and side effects of medications, pregnancy, and heart disease are also considered. The goal of treatment of hyperthyroidism is to bring thyroid hormone levels to a normal range. Doing so is intended to prevent long-term complications and relieve symptoms.
Beta blockers may be prescribed to help control symptoms of hyperthyroidism until other medications begin working. Though beta blockers do not stop thyroid hormone production, they do block the effects of thyroid hormone on the body, which can help control symptoms like tremors, rapid heartbeat, and nervousness.
Antithyroid drugs, such as methimazole and propylthiouracil, block the way the thyroid gland uses iodine to make thyroid hormone. When antithyroid drugs are used, it may take several weeks or months before thyroid hormone levels reach a normal range. Potential side effects include allergic reactions (rashes and itching), a decreased white blood cell count (which lowers resistance to infection), and, rarely, liver failure. Pregnant women should not take methimazole and should be monitored if they are taking propylthiouracil. Both drugs should only be taken in small doses among women who are breastfeeding.
In radioiodine therapy, patients are administered iodine-131, which the thyroid gland collects in the same way that it regularly collects iodine in order to make thyroid hormone. The radioactive iodine, however, will gradually destroy the cells that make the thyroid gland; it will not affect other tissues in the body. Most patients who undergo radioiodine therapy will develop hypothyroidism; this, however, is considered an acceptable outcome, as hypothyroidism is easier to treat and has fewer long-term complications than hyperthyroidism. This treatment is not used in pregnant women or women who are breast feeding.
Thyroid surgery is the least-used treatment for hyperthyroidism. It involves surgical removal of all or most of the thyroid gland. Removal of part of the thyroid may cause thyroid hormone levels to return to normal. Some patients, however, may develop hypothyroidism; these patients will need to take synthetic thyroid hormone, as will patients who have their entire thyroid removed (in this case, they will use thyroid hormone replacement for life). Thyroid surgery may be a treatment option for pregnant women who cannot tolerate antithyroid drugs, people with very large goiters, or people who have cancerous thyroid nodules. There are risks associated with thyroid surgery (damage to the parathyroid gland or laryngeal nerve, for example); more-experienced surgeons have a low rate of permanent complications.
Hypothyroidism
Hypothyroidism is a disorder where the thyroid gland doesn’t produce as much thyroid hormone as the body needs. According to the NIH, hypothyroidism affects about 5 percent of the U.S. population and women are more likely to develop it than men. The disease more commonly affects people over age 60.
Factors that may increase your chance of developing hypothyroidism include a personal or family history of thyroid disorders; another autoimmune disease (including Sjögren’s syndrome, pernicious anemia, type 1 diabetes, rheumatoid arthritis, or lupus); Turner syndrome (a genetic disorder that affects girls and women); or age older than 60 years. As well, women who have been pregnant or delivered a baby within the past six months and individuals who have received radiation to the thyroid or to the neck or chest may be at higher risk.
Causes of hypothyroidism include:
Symptoms of hypothyroidism include:
People with high cholesterol should also be tested for hypothyroidism, as this thyroid disorder can contribute to high blood cholesterol.
Diagnosing Hypothyroidism
To diagnose hypothyroidism, a doctor will likely discuss a patient’s symptoms and perform a physical examination. If he or she finds reason to suspect hypothyroidism, several tests may be used to confirm a diagnosis. Tests may also help determine the cause of the condition.
Tests for diagnosing hypothyroidism include:
Thyroid-stimulating Hormone (TSH) Test
This test detects small amounts of TSH in the blood to measure thyroid activity. When there is too much thyroid hormone in the blood, the pituitary gland stops producing TSH. In general, a TSH level reading below normal indicates hyperthyroidism and a reading above normal indicates hypothyroidism.
T4 Test
This test measures the amount of thyroid hormone circulating in the blood. In hypothyroidism, the level of T4 in the blood is below normal.
The Thyroid Autoantibody Test
The presence of thyroid autoantibodies suggests that Hashimoto’s disease is the cause of hypothyroidism (other causes are not associated with autoantibodies).
Treating Hypothyroidism
People with hypothyroidism are treated with synthetic thyroxine, a substance that is identical to the T4 made by the thyroid. Dosage will depend on the patient’s age and weight, severity of hypothyroidism, the presence of other health problems, and whether they are taking other medications that might interfere with how well the body uses thyroid hormone.
Pregnancy and Hypothyroidism
Uncontrolled hypothyroidism can increase the chance of certain complications among pregnant women. These include miscarriage, preterm delivery, and preeclampsia (a potentially serious complication that increases blood pressure). As well, untreated hypothyroidism can affect the baby’s growth and brain development. It’s important that pregnant women with hypothyroidism discuss the condition with their doctor—medications that are safe to take during pregnancy can help control hypothyroidism and prevent these complications.
American Association of Clinical Endocrinologists
Thyroid Diseases. The National Institutes of Health Web site. Available at: http://health.nih.gov/topic/ThyroidDiseases. Accessed June 2010.
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