Hyperthyroidism is overactivity of the thyroid gland that leads to high levels of thyroid hormones and speeding up of vital body functions.

• Graves' disease is the most common cause of hyperthyroidism.
• Heart rate and blood pressure may increase, heart rhythms may be abnormal, and people may sweat excessively, feel nervous and anxious, have difficulty sleeping, and lose weight without trying.
• Blood tests can confirm the diagnosis.
• Usually, methimazoleSome Trade Names
  TAPAZOLE
  or propylthiouracil can control hyperthyroidism.

Hyperthyroidism affects about 1% of people in the United States. It can occur at any age but is more common in women during menopause and after childbirth.

Causes

The most common causes include

• Graves' disease
• Thyroiditis

Other causes of hyperthyroidism include growths within the thyroid that cause the thyroid to produce too much thyroid hormone (toxic thyroid nodules) and overstimulation due to an overactive pituitary gland.

Graves' disease, the most common cause of hyperthyroidism, is an autoimmune disorder caused by an abnormal protein (antibody) in the blood that stimulates the thyroid to produce and secrete excess thyroid hormones into the blood. This cause of hyperthyroidism is often hereditary and almost always leads to enlargment of the thyroid.

Thyroiditis is inflammation of the thyroid gland. In subacute thyroiditis, silent lymphocytic thyroiditis, and, much less often, Hashimoto's thyroiditis, hyperthyroidism occurs as stored hormones are released from the inflamed gland. Hypothyroidism usually follows because the levels of stored hormones are depleted. Finally, the gland usually returns to normal function.

A toxic (hyperfunctional) thyroid nodule (adenoma) is an area of abnormal local tissue growth within the thyroid gland. This abnormal tissue produces thyroid hormones even without stimulation by thyroid-stimulating hormone (TSH). Thus, a nodule escapes the mechanisms that normally control the thyroid gland and produces thyroid hormones in large quantities. Toxic multinodular goiter (Plummer's disease), in which there are many nodules, is uncommon in adolescents and young adults and tends to become more common with aging.

Drugs and iodine can cause hyperthyroidism. Drugs include amiodaroneSome Trade Names
CORDARONE
, interferon-alpha, and, rarely, lithiumSome Trade Names
LITHOBID
. Excess iodine, as may occur in people taking certain expectorants, or iodine-containing contrast agents for x-ray studies may cause hyperthyroidism.

An overactive pituitary gland can produce too much TSH, which in turn leads to overproduction of thyroid hormones. However, this is an extremely rare cause of hyperthyroidism.

Symptoms

Most people with hyperthyroidism have an enlarged thyroid gland (goiter). The entire gland may be enlarged, or nodules may develop within certain areas. The gland may be tender and painful.

Symptoms of hyperthyroidism, regardless of the cause, reflect the speeding up of body functions: increased heart rate and blood pressure, abnormal heart rhythms (arrhythmias), excessive sweating and feeling too warm, hand tremors (shakiness), nervousness and anxiety, difficulty sleeping (insomnia), weight loss despite increased appetite, increased activity level despite fatigue and weakness, and frequent bowel movements, occasionally with diarrhea. Older people with hyperthyroidism may not develop these characteristic symptoms but have what is sometimes called apathetic or masked hyperthyroidism, in which they become weak, confused, withdrawn, and depressed. Hyperthyroidism can cause changes in the eyes. A person with hyperthyroidism may appear to be staring.

If the cause of hyperthyroidism is Graves' disease, eye symptoms include puffiness around the eyes, increased tear formation, irritation, and unusual sensitivity to light. Two distinctive additional symptoms may occur: bulging eyes (exophthalmos or proptosis—see Eye Socket Disorders: Symptoms) and double vision (diplopia—see Symptoms of Eye Disorders: Vision, Double). The eyes bulge outward because of inflammation in the orbits behind the eyes. The muscles that move the eyes become inflamed and unable to function properly, making it difficult or impossible to move the eyes normally or to coordinate eye movements, resulting in double vision. The eyelids may not close completely, exposing the eyes to injury from foreign particles and dryness. These eye changes may begin before any other symptoms of hyperthyroidism, providing an early clue to Graves' disease, but most often occur when other symptoms of hyperthyroidism are noticed. Eye symptoms may even appear or worsen after the excessive thyroid hormone secretion has been treated and controlled.

Exophthalmos

When Graves' disease affects the eyes, there may also be thickening of the skin, usually over the shins, which has the texture of an orange-peel. The thickened area may be itchy and red and feels hard when pressed with a finger. As with deposits behind the eyes, this problem may begin before or after other symptoms of hyperthyroidism are noticed.

Spotlight on Aging
Hyperthyroidism affects about the same percentage of older people as younger people—about 1%. However, hyperthyroidism is often more serious among older people because they tend to have other disorders as well. Hyperthyroidism in older people often results from Graves' disease. Almost as often, hyperthyroidism is caused by the gradual growth of many small lumps in the thyroid gland (toxic thyroid nodules). Some drugs can cause hyperthyroidism as well. The most common is amiodaroneSome Trade Names CORDARONE , a drug used to treat heart disease but which may stimulate or damage the thyroid gland. Hyperthyroidism can cause many vague symptoms that can be attributed to other conditions. Typically, symptoms differ between older and younger people. Among older people, the most common symptoms are weight loss and fatigue. The heart rate may or may not be increased, and the eyes usually do not bulge. Older people are also more likely to have abnormal heart rhythms (such as atrial fibrillation), other heart problems (such as angina and heart failure), and constipation. Occasionally, older people sweat profusely, become nervous and anxious, and have hand tremors and frequent bowel movements or diarrhea.

Diagnosis

Doctors usually suspect hyperthyroidism on the basis of the symptoms. Blood tests are used to confirm the diagnosis. Often, testing begins with measurement of TSH. If the thyroid gland is overactive, the level of TSH is low. However, in rare cases in which the pituitary gland is overactive, the level of TSH is normal or high. If the level of TSH in the serum is low, doctors measure the levels of the thyroid hormones in the blood. If there is a question of whether Graves' disease is the cause, doctors check a sample of blood for the presence of antithyroid antibodies. More specific antibodies can be measured, but such a test is rarely needed.

If a thyroid nodule is suspected as the cause, a thyroid scan will show whether the nodule is overactive, that is, whether it is producing excess hormones. Such a scan may also help doctors in their evaluation of Graves' disease. In a person with Graves' disease, the scan shows the entire gland to be overactive, not just one area. In thyroiditis, the scan shows low activity.

Prognosis and Treatment

Treatment of hyperthyroidism depends on the cause. In most cases, the problem causing hyperthyroidism can be cured or the symptoms can be eliminated or greatly reduced. If left untreated, however, hyperthyroidism places undue stress on the heart and many other organs.

Beta-blockers such as propranololSome Trade Names
INDERAL
or metoprololSome Trade Names
LOPRESSOR TOPROL-XL
help control many of the symptoms of hyperthyroidism. These drugs can slow a fast heart rate, reduce tremors, and control anxiety. Doctors therefore find beta-blockers particularly useful to control symptoms of hyperthyroidism until the person responds to other treatments. However, beta-blockers do not reduce excess thyroid hormone production. Therefore, other treatments are added to bring hormone production to normal levels.

MethimazoleSome Trade Names
TAPAZOLE
and propylthiouracil are the drugs most commonly used to treat hyperthyroidism. They work by decreasing the gland's production of thyroid hormones. Each drug is taken by mouth, beginning with high doses that are later adjusted according to blood test results. These drugs can usually control thyroid function in 6 to 12 weeks. Larger doses of these drugs may work more quickly but increase the risk of side effects. Pregnant women who take propylthiouracil or methimazoleSome Trade Names
TAPAZOLE
are closely monitored, because these drugs cross the placenta and can cause goiter or hypothyroidism in the fetus. CarbimazoleSome Trade Names
NEO-MERCAZOLE
, a drug that is widely used in Europe, is converted into methimazoleSome Trade Names
TAPAZOLE
in the body.

Did You Know? People who receive radioactive iodine should not go near infants and young children for 2 to 4 days.

Iodine, given by mouth, is sometimes used to treat hyperthyroidism. It is reserved for those in whom rapid treatment is needed. It may also be used to control hyperthyroidism until the person can have surgery to remove the thyroid. It is not used long-term.

Radioactive iodine may be given by mouth to destroy part of the thyroid gland. Very little radioactivity is introduced to the body as a whole, and most of it is delivered to the thyroid gland because the thyroid gland takes up the iodine and concentrates it. Hospitalization is rarely necessary. After treatment, the person should probably not be near infants and young children for 2 to 4 days and should sleep in a separate bed separated at least 6 feet (about 2 meters) from the partner. No special precautions are needed in the workplace. Pregnancy should be avoided for about 6 months. People who have had radioactive iodine treatment may set off radiation alarms at airports and sometimes other places for several weeks after treatment and, therefore, should carry a doctor's note describing their treatment if they travel on public transportation.

Some doctors try to adjust the dose of radioactive iodine to destroy only enough of the thyroid gland to bring its hormone production back to normal, without reducing thyroid function too much. Other doctors use a larger dose to completely destroy the thyroid. Most of the time, people who undergo this treatment must take thyroid hormone replacement therapy for the rest of their life (see Thyroid Gland Disorders: Treatment). Although concerns have been raised that radioactive iodine may cause cancer, an increased risk of cancer in people who have had radioactive iodine treatment has never been confirmed. Radioactive iodine is not given to pregnant or nursing women because it crosses the placenta and enters the milk and may destroy the fetus's or breastfed infant's thyroid gland.

Thyroid Storm
Thyroid storm, which is sudden extreme overactivity of the thyroid gland, is a life-threatening emergency. All body functions are accelerated to dangerously high levels. Severe strain on the heart can lead to a life-threatening irregular heartbeat (arrhythmia), extremely fast pulse, and shock. Thyroid storm may also cause fever, extreme weakness, restlessness, mood swings, confusion, altered consciousness (even coma), and an enlarged liver with mild jaundice (a yellowish discoloration of the skin and the whites of the eyes). Thyroid storm is generally caused by untreated or inadequately treated hyperthyroidism and can be triggered by infection, injury, surgery, poorly controlled diabetes, pregnancy or labor, or other stresses. Also, thyroid storm can occur when drugs being used to treat thyroid problems are stopped. It is rare in children.

Surgical removal of the thyroid gland, called thyroidectomy, is a treatment option for young people with hyperthyroidism. Surgery is also an option for people who have a very large goiter as well as for those who are allergic to or who develop severe side effects from the drugs used to treat hyperthyroidism. Hyperthyroidism is permanently controlled in more than 90% of people who choose this option. Hypothyroidism often occurs after surgery, and people then have to take replacement thyroid hormone for the rest of their life. Rare complications of surgery include paralysis of the vocal cords and damage to the parathyroid glands (the tiny glands behind the thyroid gland that control calcium levels in the blood).

In Graves' disease, additional treatment may be needed for the eye and skin symptoms. Eye symptoms may be helped by elevating the head of the bed, by applying eye drops, by sleeping with the eyelids taped shut, and, occasionally, by taking selenium or diuretics (drugs that hasten fluid excretion). Double vision may be helped by using eyeglass prisms. Finally, corticosteroids taken by mouth, x-ray treatment to the orbits, or eye surgery may be needed if the eyes are severely affected. Corticosteroid creams or ointments can help relieve the itching and hardness of the abnormal skin. Often the problem disappears without treatment months or years later.

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Drugs Used to Treat Hyperthyroidism Drug Some Side Effects Comments Thionamides CarbimazoleSome Trade Names NEO-MERCAZOLE MethimazoleSome Trade Names TAPAZOLE Propylthiouracil Allergic reactions (usually rashes) Nausea Loss of taste Infection (rare) due to a low white blood cell count Liver dysfunction Joint aching Decrease the production of thyroid hormones Nonmetallic element Iodine Rash Decreases the production and release of thyroid hormones Radioactive isotope Radioactive iodine Hypothyroidism Destroys the thyroid gland Beta-blockers AtenololSome Trade Names TENORMIN MetoprololSome Trade Names LOPRESSOR TOPROL-XL PropranololSome Trade Names INDERAL In people with lung disease, may cause wheezing Can worsen peripheral vascular disease Can cause depression May reduce blood pressure (hypotension) Block many of the stimulating effects of excess thyroid hormones on other organs

Last full review/revision May 2012 by Jerome M. Hershman, MD