Glossary

antibodies: Substances naturally produced in your body that protect it from harmful viruses and bacteria. Antibodies are made by white blood cells called B cells.

antithyroid drugs: A class of drugs that are sometimes prescribed to block the thyroid gland's ability to make hormone, thus reducing the level of thyroid hormone in your body.

atherosclerosis: A condition characterized by narrowed, hardened arteries, a precursor to heart disease and stroke.

atrial fibrillation: An unusually rapid, disorganized heart rhythm originating in the heart's upper chambers. It is sometimes a sign of hyperthyroidism, particularly in older people.

autoimmune disease: A disease that develops when the body's immune system attacks its own tissues, mistakenly perceiving them as foreign.

beta blockers: Drugs used primarily to treat hypertension, angina, and coronary artery disease, but also to relieve heart-related symptoms in patients with hyperthyroidism.

bioavailability: In reference to thyroid hormone medication, the amount of thyroid hormone available for use by the body with any given formulation.

congestive heart failure: A condition that results from decreased blood flow to muscles and organs throughout the body. Ineffective pumping of the heart also causes blood to back up into the veins that return blood to the heart. Blood backs up into the lungs, which become congested with fluid. Hyperthyroidism can precipitate it, and hypothyroidism can contribute to it.

desiccated thyroid: A formula of animal thyroid gland that has been dried and powdered. "Desiccate" means to dry out.

dietary supplements: Over-the-counter vitamins, minerals, herbs, or any other substances that increase total dietary intake.

euthyroid: A term used to describe normal thyroid status.

exophthalmos: A protrusion or bulging of the eye that occurs with Graves' eye disease. Tissues behind the eye swell, forcing the eyeball forward. Also called proptosis.

goiter: An enlarged thyroid gland that creates a lump protruding from the neck. It is commonly found when the thyroid produces too much or too little thyroid hormone, although sometimes it is present when thyroid levels are normal.

Graves' disease: An autoimmune disease that causes the thyroid gland to overproduce thyroid hormone.

Graves' eye disease: A condition that can occur with Graves' disease that is typically characterized by swollen, bulging, red eyes that appear to stare, and sometimes double vision and vision loss. Also called thyroid eye disease.

Hashimoto's thyroiditis: An autoimmune condition that is the leading cause of hypothyroidism in the United States. Two types of antibodies, called antithyroid peroxidase (anti-TPO) and antithyroglobulin (anti-Tg), promote the destruction of thyroid cells, making them unable to produce adequate amounts of thyroid hormone.

hyperthyroidism: A disease that occurs when the thyroid produces more thyroid hormone than your body needs, thereby abnormally speeding up your metabolism.

hypothalamus: A section of the brain that releases thyrotropin-releasing hormone (TRH), which stimulates the pituitary gland to produce thyroid-stimulating hormone (TSH). This network of communication between the hypothalamus, pituitary, and thyroid glands is referred to as the hypothalamic-pituitary-thyroid, HPT axis.

hypothyroidism: A disease that occurs when the thyroid fails to produce enough thyroid hormone to meet your body's needs, thereby slowing your metabolism.

iodides: Salt compounds containing iodine that are used to control severe hyperthyroidism in special circumstances. They work by decreasing the thyroid gland's production and secretion of thyroid hormone.

levothyroxine sodium: The active ingredient in synthetic thyroxine (T4) pills; see thyroxine.

liothyronine sodium: The active ingredient in synthetic triiodothyronine (T3) pills; see triiodothyronine.

multinodular goiter: A goiter that contains more than one lump or nodule. This type of goiter can evolve into a toxic nodular goiter and cause hyperthyroidism if the nodules are actively producing thyroid hormone.

nodule: A lump on the thyroid gland that sometimes contains active thyroid cells that produce thyroid hormone. Most nodules take up less iodine than normal thyroid tissue and make little, if any, thyroid hormone. Ninety percent of thyroid nodules appear "cold" (demonstrate less than normal function) on thyroid tests that use radioactive materials.

nutraceuticals: Dietary supplements containing concentrated forms of a presumed bioactive substance originally derived from food and used to enhance health in dosages exceeding those obtainable from normal foods.

orbital irradiation: X-ray treatment to the eye used in more serious cases of Graves' eye disease.

parathyroid glands: Glands responsible for controlling calcium and influencing bone metabolism. There are usually four of them, located behind the thyroid.

pituitary gland: The master gland, located at the base of the brain, that controls and regulates the thyroid and other glands throughout the endocrine system.

proptosis: A bulging or protrusion of the eye that occurs with Graves' eye disease when tissues behind the eye swell, forcing the eye forward. Also called exophthalmos.

radioactive iodine: A radioactive form of iodine that can be used as a tracer during a radioactive iodine uptake test or a radioactive thyroid scan. Much larger amounts are used in the treatment of hyperthyroidism.

subacute thyroiditis: A painful version of thyroiditis caused by viral infection of the thyroid that causes symptoms that may mimic the flu, including fever, muscle aches and pains, and a painful, swollen thyroid gland. Also called de Quervain's thyroiditis.

tachycardia: An abnormally fast heart rate that tops 100 beats per minute. It can be a sign of hyperthyroidism.

thyroidectomy: A surgical procedure to remove all or part of the thyroid.

thyroiditis: Inflammation of the thyroid. Types of thyroiditis include Hashimoto's thyroiditis, subacute thyroiditis, postpartum thyroiditis, and silent thyroiditis.

thyroid-stimulating hormone (TSH): A hormone secreted into the bloodstream by the pituitary gland that stimulates the thyroid gland. Normally, the amount of hormone produced by the thyroid gland depends on how much TSH is in the blood. Doctors measure levels of TSH to determine whether a person's thyroid hormone levels are normal.

thyrotoxicosis: The presence of too much thyroid hormone in the body. This may be caused by an overproductive thyroid, inflammation of the thyroid, or taking too much thyroid hormone.

thyroxine (T4): One of two major types of thyroid hormone manufactured by the thyroid gland. It contains four iodine atoms.

toxic nodular goiter: An enlarged thyroid gland with nodules that produce excess thyroid hormone. This type of goiter is responsible for hyperthyroidism in many people over 60.

triiodothyronine (T3): One of two major types of thyroid hormone manufactured by the thyroid gland. It contains three iodine atoms. Outside the thyroid gland, the liver and other organs convert T4 to T3.