Patient information: Hyperthyroidism

HYPERTHYROIDISM OVERVIEW

Hyperthyroidism is the medical term for an overactive thyroid (hyper = excessive). In people with hyperthyroidism, the thyroid gland produces too much thyroid hormone. When this occurs, the body's metabolism is increased, which can cause a variety of symptoms.

This topic discusses the symptoms, diagnostic tests, and treatment options for HYPERthyroidism. HYPOthyroidism is discussed in a separate topic. (See "Patient information: Hypothyroidism".)

WHAT IS THE THYROID?

The thyroid is a butterfly-shaped gland in the middle of the neck, located below the larynx (voice box) and above the clavicles (collarbones) (figure 1). The thyroid produces two hormones, triidodothyronine (T3) and thyroxine (T4) that regulate how the body uses and stores energy (also known as the body's metabolism). Thyroid function is controlled by a gland in the brain, known as the pituitary. The pituitary produces thyroid stimulating hormone (TSH), which stimulates the thyroid to produce T3 and T4.

HYPERTHYROIDISM CAUSES

The most common cause of hyperthyroidism is Graves' disease.

Graves' disease — Graves' disease results from an interaction between a person's genetic makeup (heredity) and the immune system. For reasons that are not understood, the immune system produces an antibody that stimulates the thyroid gland to produce too much thyroid hormone. This is most common in women between the ages of 20 and 40, but can occur at any age in both genders. The thyroid gland enlarges (called a goiter) and makes excessive amounts of thyroid hormone, resulting in the typical symptoms of hyperthyroidism.

Some people develop eye problems (called Graves' ophthalmopathy), which causes dry, irritated or red eyes, and double vision. Others develop swelling behind the eyes that causes the eyes to protrude, although this is less common. In its most severe form, people with Graves' ophthalmopathy can develop inflammation of the optic nerves, which can result in loss of vision.

Other causes

• One or more thyroid nodules (small growths or lumps in the thyroid gland) can produce too much thyroid hormone (the nodule is then called a hot nodule, toxic nodule, or toxic nodular goiter). (See "Patient information: Thyroid nodules".)

• Painless ("silent or lymphocytic") thyroiditis and postpartum thyroiditis are related autoimmune disorders in which the thyroid becomes temporarily inflamed and releases thyroid hormone into the bloodstream, causing hyperthyroidism. Postpartum thyroiditis can occur several months after delivery. The hyperthyroid symptoms may last for several months, often followed by several months of hypothyroid symptoms, such as fatigue, muscle cramps, bloating and weight gain.
• Subacute (granulomatous) thyroiditis is thought to be caused by a virus. It causes a painful, tender, enlarged thyroid gland. The thyroid becomes inflamed and releases thyroid hormone into the blood stream; the hyperthyroidism resolves when the viral infection improves.
• Taking too much thyroid hormone medication for hypothyroidism

HYPERTHYROIDISM SYMPTOMS

Most people with hyperthyroidism have symptoms, including one or more of the following:

• Anxiety and irritability
• Weakness (in particular of the upper arms and thighs, making it difficult to lift heavy items or climb stairs)
• Tremors (of the hands)
• Perspiring more than normal; difficulty tolerating hot weather
• Rapid or irregular heartbeats
• Fatigue
• Weight loss in spite of a normal or increased appetite
• Frequent bowel movements.

In addition, some women have irregular menstrual periods or stop having their periods altogether. This can be associated with infertility. Men may develop enlarged or tender breasts, or erectile dysfunction, which resolves when hyperthyroidism is treated.

HYPERTHYROIDISM DIAGNOSIS

If hyperthyroidism is suspected, blood tests will be ordered to measure the amount of thyroid hormone and thyroid-stimulating hormone (TSH). Typically, the thyroid hormone level is high and the TSH level is low. A thyroid scan may also be recommended to help determine the type of hyperthyroidism (Graves' disease, toxic nodular goiter, or thyroiditis).

HYPERTHYROIDISM TREATMENT

Hyperthyroidism can be treated using medicine, radiation, or surgery. Many factors, such as the person's age and the severity and type of hyperthyroidism, are important in determining which treatment is best.

Medications — The two main types of medicines used to treat hyperthyroidism are antithyroid drugs and beta-blockers. (See "Patient information: Antithyroid drugs".)

Antithyroid drugs — Antithyroid drugs, such as methimazole (MMI or Tapazole) and propylthiouracil (PTU), work by decreasing the production of thyroid hormone. Both are very effective, but methimazole is generally preferred because of a rare risk of serious side effects with PTU.

For pregnant women, PTU is the preferred drug during the first trimester. After the first trimester, methimazole is preferred. (See "Patient information: Antithyroid drugs".)

These medications are usually used short-term in Graves' disease and toxic nodular goiter (prior to treatment with radioiodine or surgery). Long-term treatment is necessary in patients with Graves' disease. Most people start feeling better after several weeks on the medication, although many clinicians recommend continuing to take it for one to two years. After that time, there is a 20 to 30 percent chance of having a remission. Some patients can relapse years later, and most people will need to eventually consider permanent treatment with radioactive iodine or surgery.

Antithyroid drugs have some minor side effects, such as rash, hives, painful joints, fever, and stomach upset. A more serious complication called agranulocytosis (lack of white blood cells) can occur, but this is very rare.

While taking antithyroid drugs, a blood test for thyroid hormone will be done every four to six weeks until the hyperthyroidism is under control.

Beta-blockers — Beta-blockers, such as atenolol, are often started as soon as the diagnosis of hyperthyroidism is made. While beta-blockers do not reduce thyroid hormone production, they can control many of the bothersome symptoms, such as rapid heart rate, tremors, anxiety, and heat intolerance. Once the hyperthyroidism is under control (by antithyroid drugs, surgery, or radioactive iodine), the beta-blocker is stopped.

Radioactive iodine — Destroying the thyroid with radiation, called radioiodine ablation, is a permanent way to resolve hyperthyroidism. The amount of radiation used is small and does not cause cancer. This is the most widely used treatment in the United States.

Radioiodine is given in liquid or capsule form, and it works by attacking and destroying much of the thyroid tissue. This takes about 6 to 18 weeks. People with severe symptoms, older adults, and people with heart problems should first be treated with an antithyroid drug to control symptoms. Most patients who receive radioiodine develop hypothyroidism and need to take thyroid hormone supplements for the rest of their lives. (See "Patient information: Hypothyroidism".)

As with most treatments, there are some risks:

• Sometimes, after apparently successful treatment, the condition returns and further treatment is needed.
• About 20 percent of those who use radioiodine treatment require a second dose. These people usually have severe hyperthyroidism or a very large goiter.
• Occasionally, people whose hyperthyroidism is caused by Graves' disease may find that their eye symptoms worsen after therapy.

People who undergo this therapy should avoid close physical contact, especially with young children and pregnant women, for three to seven days after treatment because of the possibility of exposing them to low doses of radiation. This can be difficult for parents of young children. Patients will need to see their clinician on a regular basis after treatment to have thyroid hormone levels checked and monitor for hypothyroidism or recurrent hyperthyroidism.

Surgery — Although surgical removal of the thyroid is a permanent cure for hyperthyroidism, it is used far less often than antithyroid drugs or radioactive iodine because of the risks (and expense) associated with thyroid surgery. The risks include damage to the nerves of the voice box and parathyroid glands, which regulate calcium.

However, surgery is recommended when:

• A large goiter obstructs the airways, making it difficult to breathe.
• Antithyroid drugs are not well tolerated, and the individual is unwilling to use radioiodine.

The follow-up after surgery is similar to that for radioactive iodine treatment: regular appointments to test thyroid hormone levels in the blood and to watch for signs of hypo- and hyperthyroidism. Most patients develop hypothyroidism and require ongoing thyroid hormone supplements. (See "Patient information: Hypothyroidism".)

PREGNANCY AND HYPERTHYROIDISM

Women who take antithyroid drugs and want to become pregnant should discuss this with their healthcare provider. There are risks to the mother and fetus if hyperthyroidism is not well controlled; these risks can be avoided or minimized with frequent monitoring and medication adjustment throughout the pregnancy.

Use of radioactive iodine treatment before conception usually eliminates the need for antithyroid drugs and any possible associated risks. A woman should wait at least six months after radioactive iodine treatment before trying to become pregnant.

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two people are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.

This discussion will be updated as needed every four months on our web site (www.uptodate.com/patients). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.

Some of the most pertinent include:

Patient Level Information:
Patient information: Hypothyroidism
Patient information: Thyroid nodules
Patient information: Antithyroid drugs

Professional Level Information:
Amiodarone and thyroid dysfunction
Beta blockers in the treatment of hyperthyroidism
Bone disease with hyperthyroidism and thyroid hormone therapy
Cardiovascular effects of hyperthyroidism
Causes and clinical manifestations of hyperthyroidism during pregnancy
Clinical manifestations and diagnosis of hyperthyroidism in children and adolescents
Diagnosis and treatment of hyperthyroidism during pregnancy
Diagnosis of hyperthyroidism
Disorders that cause hyperthyroidism
Evaluation and management of neonatal Graves' disease
Exogenous and ectopic hyperthyroidism
Iodinated radiocontrast agents in the treatment of hyperthyroidism
Iodine in the treatment of hyperthyroidism
Neurologic manifestations of hyperthyroidism and Graves' disease
Overview of the clinical manifestations of hyperthyroidism in adults
Radioiodine in the treatment of hyperthyroidism
Subclinical hyperthyroidism
Surgery in the treatment of hyperthyroidism
Thionamides in the treatment of Graves' disease
Treatment of Graves' hyperthyroidism

A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable.

• National Library of Medicine

      (www.nlm.nih.gov/medlineplus/healthtopics.html)

• The American Thyroid Association

     (www.thyroid.org)

• Thyroid Foundation of Canada

      (www.thyroid.ca)

• The Hormone Foundation

      (www.hormone.org/public/thyroid.cfm, available in English and Spanish)

Patient Support — There are a number of online forums where patients can find information and support from other people with similar conditions.

• About.com Thyroid Conditions Forum

      (http://thyroid.about.com/forum)

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