• Also Known As:
  • Hypothyroidism
  • Hyperthyroidism
  • Thyroid Cancer
  • Goiter
  • Thryroiditis
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What is the thyroid and what are thyroid diseases?

The thyroid is a small, butterfly-shaped gland that lies flat across the windpipe at the base of the throat. This gland plays a very important role in controlling the body’s metabolism by producing thyroid hormones. Most of the hormone produced by the thyroid is thyroxine (T4). The other major thyroid hormone is called triiodothyronine (T3).

These thyroid hormones travel through the blood to every part of the body and tell the cells in the body how fast to use energy and produce proteins. The thyroid gland also makes calcitonin, a hormone that helps to regulate calcium levels in the blood by preventing the breakdown (reabsorption) of bone and increasing calcium elimination from the kidneys.

The body has an elaborate feedback system to control the amount of T4 and T3 in the blood. The feedback system also includes thyroid-stimulating hormone (TSH), made by the pituitary gland, and its regulatory hormone, thyrotropin-releasing hormone (TRH), which comes from the hypothalamus.

  • When thyroid hormone levels decrease, the hypothalamus releases TRH, which in turn causes the pituitary gland to release TSH.
  • TSH stimulates the thyroid gland to produce and release T4 (primarily) and T3. Inside the thyroid, most of the T4 is stored bound to a protein called thyroglobulin. When the need arises, the thyroid gland produces more T4 and/or releases some of what is stored.
  • As thyroid hormone levels increase in the blood, the hypothalamus and pituitary gland produce less hormones, and the thyroid produces less T4 and T3.

Under normal circumstances, this feedback system regulates thyroid activity to maintain relatively stable levels of thyroid hormones in the blood.

In the blood, most T4 and T3 are bound to a protein called thyroxine-binding globulin (TBG). The protein-bound forms are thought to be inactive. The small amounts that are unbound, called free T4 or free T3, are the active forms of the hormone. T4 is converted to the much more active T3 in the liver and other tissues. T3 is primarily responsible for controlling the rate of body functions.

Thyroid diseases are conditions that affect the thyroid, and some affect the amount of hormones the thyroid produces. The American Thyroid Association estimates that 20 million Americans have some form of thyroid disease, and about 60% of those with thyroid disease do not know it. Women are more likely than men to have thyroid problems, with 1 in 8 developing a thyroid disorder during her life.


About Thyroid Diseases

Types and Causes

Some examples of thyroid disorders and causes are described below.

Hypothyroidism (underactive thyroid)—this condition is caused by diseases that result in little thyroid hormone being produced, which results in slowing of body functions. (See the section below on Signs and Symptoms.) Specific causes include:

  • Hashimoto thyroiditis—this is the most common cause of hypothyroidism in the United States. It is a long-term (chronicautoimmune condition. The immune system, which normally protects against infections, mistakenly targets the thyroid, causing inflammation and damage. Immune proteins called autoantibodies are usually present in the blood.
  • Surgery to remove part or all the thyroid—this procedure may be done as part of treatment for thyroid nodulesthyroid cancer, or Graves disease, for example.
  • Radiation treatment—like surgery, this may be used to treat some thyroid conditions such as thyroid cancer or Graves disease. It may also be used to treat cancers (e.g., lymphoma, head and neck cancers). Radiation treatments can damage the thyroid and ultimately affect its function.
  • Several medications (e.g., lithium) can cause or worsen hypothyroidism.
  • Congenital hypothyroidism—this condition affects infants from birth. It is most commonly due to a thyroid gland that is missing, only partially developed, or located in an abnormal part of the body. The rest of the cases are due to a normal-sized or enlarged thyroid that does not function properly or produce enough thyroid hormone. Left untreated, this condition can cause delays in physical and intellectual development. Screening for hypothyroidism is performed in most countries as part of newborn blood screening programs, since early detection and treatment can limit long-term damage.
  • Iodine deficiency or excess—the thyroid requires iodine to make thyroid hormones. Lack of this element (as iodide), especially in the diet, limits the ability of the thyroid gland to make enough thyroid hormone and can contribute to hypothyroidism. This condition is relatively uncommon in the U.S. Conversely, too much iodine can cause the thyroid to shrink and produce less hormone.
  • Pituitary disorder—these are rare disorders that can lead to too little TSH, which in turn can lead to too little thyroid hormone. Damage can be caused by, for example, a tumor, radiation, or surgery.

Hyperthyroidism (overactive thyroid)—this condition is caused by too much thyroid hormone, which speeds up body functions. (See the section below for signs and symptoms.) Specific types and causes of hyperthyroidism include:

  • Graves disease—this is the most common cause of hyperthyroidism. It is a long-term (chronic) autoimmune disorder. The immune system, which normally protects against infections, produces immune proteins called autoantibodies that act like TSH and stimulate the thyroid to produce too much thyroid hormone. This autoantibody is called thyroid-stimulating immunoglobulin (TSI).
  • Thyroid tumor—a small, usually benign tumor may produce excess thyroid hormone.
  • Multinodular goiter—a condition that develops gradually over time when iodine intake is chronically insufficient. This causes the thyroid to enlarge and for multiple nodules to develop. After many years, when iodine intake becomes adequate, one or more of the nodules may make too much thyroid hormone.
  • Abnormal thyroid stimulation—a tumor made up of the cells that produce TSH can result in excess thyroid hormone production. Also, human chorionic gonadotropin (hCG), the hormone that supports the growth of the fetus in pregnancy, can act like TSH and sometimes produce hyperthyroidism in pregnant women, especially if their hCG levels are very high.

Goiter—this refers to an enlarged thyroid gland. Many different conditions can cause a goiter, including Graves disease, Hashimoto thyroiditis, multinodular goiter, and some thyroid tumors. While goiters are usually painless, they may compress vital structures of the neck, including the windpipe and esophagus, making it difficult to breathe and swallow.

Thyroiditis—this is an inflammation of the thyroid gland. Depending on the cause, it can be acute but temporary, or long-lasting. The inflammation may lead to the thyroid producing too little thyroid hormone and hypothyroidism, or to the release of too much thyroid hormone by the thyroid and hyperthyroidism. It may be painful, feeling like a sore throat, or painless. Thyroiditis may be due to an autoimmune disorder (especially Hashimoto thyroiditis), an infection by a virus or bacteria, radiation (as a medical treatment for cancer), drugs (e.g., interferon, amiodarone, lithium) or due to an unknown cause (idiopathic). About 10% of women may experience inflammation of the thyroid after giving birth (postpartum thyroiditis).

Thyroid nodules—these are abnormal growths of thyroid tissue that form a swelling or lump within the thyroid gland. These nodules can happen at any age but become increasingly common as you get older and are more common in women than men. Most thyroid nodules do not cause symptoms and are found by chance, such as during an imaging scan for another condition or during a neck evaluation as part of a routine health exam. Occasionally, you may notice a lump in your neck and bring it to your healthcare practitioner’s attention. Once found, both the nodule and the thyroid gland need to be evaluated. More than 90% of thyroid nodules are not harmful (benign), but a small percentage are cancerous.

Thyroid cancer—this is the uncontrolled growth of thyroid cells. Thyroid cancer is most commonly suspected when your healthcare practitioner notices a change in the size or shape of your thyroid gland, or you or your practitioner feels a lump or swelling in the neck during a physical exam. Because many other conditions can cause changes in thyroid gland size, shape or texture, further evaluations such as blood tests for thyroid function, ultrasound imaging, or other tests are often required. Most thyroid cancers are found early, when they are most treatable, and have a good outlook (prognosis). Often, they can be cured, especially if they have not spread to other areas of the body.

The American Cancer Society estimates that about 52,000 new cases are diagnosed in the U.S. each year, and about 2,000 people die of the disease.

The main types of thyroid cancers include:

  • Papillary thyroid cancer—this is the most common form of thyroid cancer. About 80% of thyroid cancer cases are papillary.
  • Follicular thyroid cancer—this is the second most common thyroid cancer, accounting for about 10% of cases.
  • Medullary thyroid cancer—accounts for up to 4% of thyroid cancers and develops from the cells that make calcitonin. It can spread beyond the thyroid and be difficult to treat if it is not discovered early.
  • Anaplastic thyroid cancer—this type accounts for about 2% of thyroid cancers. It tends to spread quickly and is difficult to treat successfully.

For more details, see the article on Thyroid Cancer.

Thyroid hormone resistance syndrome—this is a rare genetic disorder caused by a genetic change (mutation) in the thyroid hormone receptor. In this disorder, some body tissues do not respond normally to thyroid hormones. There may be no symptoms or symptoms of hypothyroidism or hyperthyroidism.

Signs and Symptoms

Signs and symptoms vary depending on the type of thyroid disease. Signs and symptoms of a particular thyroid disease can vary from person to person and can be non-specific—they can occur with other conditions unrelated to the thyroid. You can also have few or no noticeable symptoms at first, but then they worsen over time.

Some examples of signs and symptoms of hyperthyroidism include:

  • Rapid heart rate
  • Increased sweating
  • Trouble tolerating heat
  • Anxiety, nervousness
  • Weight loss
  • Difficulty sleeping
  • Hand tremors
  • Muscle weakness
  • Fatigue
  • Sometimes more frequent bowel movements
  • Light sensitivity, visual disturbances
  • For women, less frequent or lighter menstrual periods
  • Some uncommon problems that can affect the eyes include puffiness around the eyes, dryness, irritation, excessive tearing, light sensitivity, blurry or double vision, and, in some cases, bulging of the eyes.

Some examples of signs and symptoms of hypothyroidism include:

  • Slowed heart rate
  • Weight gain
  • Dry skin
  • Enlarged thyroid (goiter)
  • Constipation
  • Puffy face
  • Thinning hair, hair loss
  • Muscle weakness
  • Muscle and joint pain
  • In women, heavy or irregular menstrual periods
  • Fertility problems
  • Trouble tolerating cold
  • Fatigue
  • Depression
  • Forgetfulness

A lump or swelling on your thyroid noticed by you or your healthcare practitioner may be a sign of a thyroid nodule, which can be benign or cancerous. Testing is required to help determine the cause of the swelling or lump.

Other signs and symptoms of thyroid cancer may include:

  • Voice changes, including increasing hoarseness
  • Trouble breathing
  • Trouble swallowing
  • Swollen neck lymph nodes without an upper respiratory infection


A physical exam and a complete medical history are important in diagnosing a thyroid disease. A combination of laboratory tests and imaging scans may be used to evaluate your thyroid and help make a diagnosis.

Laboratory Tests

Depending on the initial test results and the suspected thyroid disease, additional blood tests may be ordered. Examples include:

  • Thyroid antibodies—to help diagnose autoimmune thyroid conditions and tell the difference between the types of thyroiditis
    • Thyroid peroxidase antibody (TPO)—the most common test for autoimmune thyroid disease. It can be detected in Graves disease or Hashimoto thyroiditis.
    • Thyroglobulin antibody (TGAb)— this antibody targets thyroglobulin, the storage form of thyroid hormones.
    • Thyroid-stimulating hormone receptor antibodies (TSHRAb)—includes two types of autoantibodies, thyroid stimulating immunoglobulin (TSI) and thyroid binding inhibitory immunoglobulin (TBII).
  • Calcitonin—to help detect elevated blood calcitonin levels, which can occur with medullary thyroid cancer.
  • Thyroglobulin—to monitor the treatment of papillary or follicular thyroid cancer and to detect recurrence.

Biopsy—this is often a fine-needle aspiration biopsy (FNA, FNAB), a procedure that involves inserting a very thin needle into the thyroid and withdrawing cells and/or fluid from a thyroid nodule or other area that the healthcare practitioner wants to examine. An ultrasound is used to guide the needle into the correct position. If the diagnosis (benign vs. malignant) is unclear, examining the biopsy material with molecular tests for mutations in certain genes (e.g., BRAF, RAS) or fusion genes (e.g., RET/PTC, Pax8-PPARG) may help. (See the article on Anatomic Pathology for more general information on biopsies.)

Newborns are routinely screened within days of birth for congenital hypothyroidism. (Read the article on Newborn Screening for more on this.)

Screening for thyroid disease in asymptomatic adults is controversial, and there is no consensus in the medical community as to who would benefit from screening and at what age to begin. The U.S. Preventive Services Task Force has found insufficient evidence to recommend for or against routine screening for thyroid disease in asymptomatic adults. However, the American Thyroid Association and the American Association of Clinical Endocrinologists recommend that screening for hypothyroidism be considered for people over the age of 60. Because the signs and symptoms of both hypothyroidism and hyperthyroidism are similar to those seen in many common disorders, healthcare practitioners often need to rule out thyroid disease even though the patient has another problem.

Non-Laboratory Tests

Ultrasound of the thyroid gland—this is usually one of the first tests used to evaluate your thyroid if you or your healthcare practitioner detects a goiter or thyroid nodule. Results of the ultrasound may show suspicious areas or confirm that one or more nodules is present. It will also show a nodule’s location, size, shape and other characteristics.

Thyroid scans:

  • FDG-PET scan (fluorodeoxyglucose (FDG)-positron emission tomography (PET)—the role of this scan in evaluating the thyroid and helping to detect cancer is still being studied. It uses a small amount of radioactively-labeled glucose. Depending on the results, follow-up testing (e.g., ultrasound, FNA) may be done.
  • Radioactive iodine scan—this scan is not routinely done anymore because ultrasound and FNAs are very good at evaluating thyroid nodules. However, it may be done in rare cases when a person has a thyroid nodule and hyperthyroidism. Thyroid nodules that produce excess thyroid hormone (causing hyperthyroidism) take up more of the radioactively labeled iodine than normal thyroid tissue, which shows up on the scan. It may also be done after removal of the thyroid for cancer to see if any residual thyroid or cancer tissue is present.

For more on imaging studies, see the website RadiologyInfo.org.


Treatment for thyroid disease depends on the cause, severity of your symptoms, and the levels of hormone produced by your thyroid.

Hyperthyroidism treatment is aimed at reducing the hormones produced by the thyroid gland and relieving symptoms. Treatment options typically include:

  • Beta blockers, such as propranolol, may reduce the effects of thyroid hormone on the body. These medications can relieve rapid heart rate, sweating, and anxiety and minimize shaking and nervousness caused by increased hormone activity. Beta blockers work quickly and provide relief while waiting for long-term treatments to take effect.
  • Anti-thyroid drugs reduce thyroid hormone production. These are usually prescribed for no more than 1 to 2 years. For some people, normal thyroid function will continue after the drugs are stopped. For most people, additional treatment will be required.
  • A large dose of radioactive iodine may be given to destroy most or all of the thyroid gland, reducing hormone levels and eliminating the symptoms of hyperthyroidism. In some cases, this therapy is not enough to cure the disease and may need to be repeated. Over time, the thyroid gland may have decreased function and you may develop hypothyroidism.
  • Sometimes surgery is performed to remove the thyroid gland.
  • Once the thyroid has been removed or destroyed, you may need to take thyroid hormone replacement medication (levothyroxine). This is synthetic (man-made) T4 that taken as a daily pill that you will likely need to for the rest of your life.

Hypothyroidism treatment is usually straightforward:

  • No treatment may be required when you are not experiencing any significant symptoms.
  • Thyroid hormone replacement therapy is typically necessary when thyroid hormone levels are significantly decreased and you begin to experience symptoms or they worsen. You may be treated with synthetic (man-made) T4 that can be taken as a pill. This medication replaces the T4 your thyroid cannot make and you will likely need to take this medication for the rest of your life. You will be closely monitored (usually with a TSH test) and your thyroid hormone replacement therapy will be adjusted as necessary.

Most thyroid cancers, especially papillary and follicular cancers, are highly treatable. Thyroid cancer treatment depends on the type of thyroid cancer, how far it has progressed, and your individual health and preferences.

Many thyroid cancers are treated with surgery to remove all or part of the thyroid, followed by one or more therapies to kill or control remaining cancer cells, if needed. Surgery may not be done for some very small papillary carcinomas unless they grow to a large enough size. If you are treated with surgery that removes all of the thyroid, you will also require hormone replacement therapy (levothyroxine).

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