Hypothyroidism National Endocrine and Metabolic Diseases Information Service What is hypothyroidism? Pituitary Hypothyroidism is a disorder that occurs gland when the thyroid gland does not make enough thyroid hormone to meet the U.S. Department of Health and body’s needs. Thyroid hormone regulates Human Services metabolism—the way the body uses energy— and affects nearly every organ in the body. NATIONAL Without enough thyroid hormone, many INSTITUTES OF HEALTH of the body’s functions slow down. About 4.6 percent of the U.S. population age 12 and TSH older has hypothyroidism.1 What is the thyroid? Thyroid The thyroid is a 2-inch-long, butterfly-shaped gland weighing less than 1 ounce. Located in the front of the neck below the larynx, or voice box, it has two lobes, one on each side T -T of the windpipe. The thyroid is one of the 3 4 glands that make up the endocrine system. The glands of the endocrine system produce The thyroid gland makes two thyroid hormones, and store hormones and release them into T3 and T4. Thyroid hormone production is regulated the bloodstream. The hormones then travel by TSH, which is made by the pituitary gland in the through the body and direct the activity of brain. the body’s cells. The thyroid gland makes two thyroid heart and nervous system functions, body hormones, triiodothyronine (T3) and temperature, muscle strength, skin dryness, thyroxine (T4). T3 is made from T4 and is menstrual cycles, weight, and cholesterol the more active hormone, directly affecting levels. the tissues. Thyroid hormones affect Thyroid hormone production is regulated metabolism, brain development, breathing, by thyroid-stimulating hormone (TSH), which is made by the pituitary gland in the brain. When thyroid hormone levels in the blood are low, the pituitary releases more 1Golden SH, Robinson KA, Saldanha I, Anton TSH. When thyroid hormone levels are B, Ladenson PW. Prevalence and incidence of high, the pituitary responds by dropping TSH endocrine and metabolic disorders in the United production. States: a comprehensive review. Journal of Clinical Endocrinology & Metabolism. 2009;94(6):1853–1878. What causes Thyroiditis hypothyroidism? Thyroiditis causes stored thyroid hormone Hypothyroidism has several causes, including to leak out of the thyroid gland. At first, the leakage raises hormone levels in the • Hashimoto’s disease blood, leading to hyperthyroidism—when • thyroiditis, or inflammation of the thyroid hormone levels are too high––that thyroid lasts for 1 to 2 months. Most people then develop hypothyroidism before the thyroid is • congenital hypothyroidism, or completely healed. hypothyroidism that is present at birth Several types of thyroiditis can cause • surgical removal of part or all of the hyperthyroidism followed by hypothyroidism: thyroid • Subacute thyroiditis. This condition • radiation treatment of the thyroid involves painful inflammation and • some medications enlargement of the thyroid. Experts are not sure what causes subacute Less commonly, hypothyroidism is caused by thyroiditis, but it may be related to too much or too little iodine in the diet or by a viral or bacterial infection. The abnormalities of the pituitary gland. condition usually goes away on its own Hashimoto’s Disease in a few months. Hashimoto’s disease, also called chronic • Postpartum thyroiditis. This type of lymphocytic thyroiditis, is the most common thyroiditis develops after a woman cause of hypothyroidism in the United gives birth. For more information, see States.1 Hashimoto’s disease is a form of the section titled “What happens with chronic inflammation of the thyroid gland. pregnancy and thyroid conditions?” Hashimoto’s disease is also an autoimmune • Silent thyroiditis. This type of disorder. thyroiditis is called “silent” because Normally, the immune system protects it is painless, as is postpartum the body against foreign invaders—such thyroiditis, even though the thyroid as viruses and bacteria—that can cause may be enlarged. Like postpartum illness. But in autoimmune diseases, the thyroiditis, silent thyroiditis is probably immune system attacks the body’s own cells an autoimmune condition and and organs. With Hashimoto’s disease, the sometimes develops into permanent immune system attacks the thyroid, causing hypothyroidism. inflammation and interfering with its ability Congenital Hypothyroidism to produce thyroid hormones. Some babies are born with a thyroid More information about Hashimoto’s disease that is not fully developed or does not can be found in the National Endocrine and function properly. If untreated, congenital Metabolic Diseases Information Service hypothyroidism can lead to mental (NEMDIS) fact sheet Hashimoto’s Disease at retardation and growth failure. Early www.endocrine.niddk.nih.gov. treatment can prevent these complications, so most newborns in the United States are screened for hypothyroidism. 2 Hypothyroidism Surgical Removal of the Thyroid What are the symptoms of When part of the thyroid is removed, the hypothyroidism? remaining part may produce normal amounts Hypothyroidism has many symptoms that can of thyroid hormone, but some people who vary from person to person. Some common have this surgery develop hypothyroidism. symptoms of hypothyroidism are Removal of the entire thyroid always results in hypothyroidism. • fatigue Part or all of the thyroid may be surgically • weight gain removed as a treatment for • a puffy face • hyperthyroidism • cold intolerance • a large goiter, which is an enlarged • joint and muscle pain thyroid that may cause the neck to appear swollen and can interfere with • constipation normal breathing and swallowing • dry skin • thyroid nodules, which are • dry, thinning hair noncancerous tumors, called adenomas, • decreased sweating or lumps in the thyroid that can produce excess thyroid hormone • heavy or irregular menstrual periods and impaired fertility • thyroid cancer • depression Radiation Treatment of the • slowed heart rate Thyroid Radioactive iodine, a common treatment However, hypothyroidism develops slowly, for hyperthyroidism, gradually destroys so many people don’t notice symptoms of the the cells of the thyroid. Most people disease. who receive radioactive iodine treatment Symptoms more specific to Hashimoto’s eventually develop hypothyroidism. People disease are a goiter and a feeling of fullness with Hodgkin’s disease, other lymphomas, in the throat. and head or neck cancers are treated with radiation, which can also damage the thyroid. Hypothyroidism can contribute to high cholesterol, so people with high cholesterol Medications should be tested for hypothyroidism. Rarely, Some drugs can interfere with thyroid severe, untreated hypothyroidism may lead hormone production and lead to to myxedema coma, an extreme form of hypothyroidism, including hypothyroidism in which the body’s functions slow to the point that it becomes life • amiodarone, a heart medication threatening. Myxedema requires immediate • interferon alpha, a cancer medication medical treatment. • lithium, a bipolar disorder medication • interleukin-2, a kidney cancer medication 3 Hypothyroidism Who is likely to develop What happens with hypothyroidism? pregnancy and thyroid Women are much more likely than men to conditions? develop hypothyroidism. The disease is also Hypothyroidism. During pregnancy, more common among people older than hypothyroidism is usually caused by 1 age 60. Hashimoto’s disease and occurs in three to Certain factors can increase the chances of five out of every 1,000 pregnancies.2 developing thyroid disorders. People may Uncontrolled hypothyroidism raises the need more regular testing if they chance of miscarriage, preterm delivery, and • have had a thyroid problem before, such preeclampsia—a dangerous rise in blood as a goiter pressure during late pregnancy. • have had surgery to correct a thyroid Untreated hypothyroidism during pregnancy problem may also affect the baby’s growth and brain development. Thyroid medications • have received radiation to the thyroid, can help prevent these problems and are neck, or chest safe to take during pregnancy. Women • have a family history of thyroid disease with hypothyroidism should discuss their condition with their health care provider • have other autoimmune diseases, before becoming pregnant. including – Sjögren’s syndrome, characterized by Postpartum thyroiditis. This inflammation dry eyes and mouth of the thyroid gland affects about 4 to 9 percent of women in the first year after – pernicious anemia, a vitamin B12 giving birth.2 Postpartum thyroiditis is deficiency believed to be an autoimmune condition and – type 1 diabetes causes hyperthyroidism that usually lasts for – rheumatoid arthritis 1 to 2 months. – lupus, a chronic inflammatory Women with postpartum thyroiditis often condition develop hypothyroidism before the thyroid • have Turner syndrome, a genetic gland is completely healed. The condition is disorder that affects females likely to recur with future pregnancies. • are older than age 60 Postpartum thyroiditis sometimes goes • have been pregnant or delivered a baby undiagnosed because the symptoms are within the past 6 months mistaken for postpartum blues—the exhaustion and moodiness that sometimes People should get tested regularly to help follow delivery. If symptoms of fatigue uncover thyroid problems—especially subclinical problems. Subclinical means a person has no apparent symptoms. 2Ogunyemi DA. Autoimmune thyroid disease and pregnancy. emedicine website. http://emedicine. medscape.com/article/261913-overview.