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(See also Overview of the Thyroid Gland.)
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, methimazole 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.
The most common causes include
Graves disease, the most common cause of hyperthyroidism, is an autoimmune disorder. In an autoimmune disorder, the person's immune system produces antibodies that attack the body's own tissues. Usually, the antibodies damage cells and worsen their ability to function. However, in Graves disease, the antibodies stimulate the thyroid to produce and secrete excess thyroid hormones into the blood. This cause of hyperthyroidism is often hereditary and almost always leads to enlargement of the thyroid.
Thyroiditis is inflammation of the thyroid gland. The inflammation can be caused by a viral infection (subacute thyroiditis), autoimmune thyroid inflammation that occurs after childbirth (silent lymphocytic thyroiditis), and, much less often, chronic autoimmune inflammation (Hashimoto thyroiditis). At first, the inflammation causes hyperthyroidism as stored hormones are released from the inflamed gland. Later on, hypothyroidism usually follows because the levels of stored hormones are depleted. Finally, the gland usually returns to normal function.
Toxic multinodular goiter (Plummer disease), in which there are many nodules, tends to becomes common with aging but is uncommon in adolescents and young adults.
Other causes of hyperthyroidism include
A toxic (overactive) thyroid nodule (a benign tumor, or 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, a hormone produced by the pituitary gland to stimulate the thyroid gland to produce thyroid hormones). Thus, a nodule escapes the mechanisms that normally control the thyroid gland and produces thyroid hormones in large quantities.
Drugs and iodine can cause hyperthyroidism. Drugs include amiodarone, interferon-alpha, and, rarely, lithium. 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.
Most people with hyperthyroidism have an enlarged thyroid gland (goiter). The entire gland may be enlarged, or nodules may develop within certain areas. If people have subacute thyroiditis, 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
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:
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.
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.
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.
Thyroid storm is diagnosed by a person's symptoms and examination findings. People are treated with drugs used to treat hyperthyroidism and with measures to treat complications (such as fever or altered consciousness), typically in an intensive care unit.
Doctors usually suspect hyperthyroidism on the basis of the symptoms. Thyroid function 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 blood 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 antibodies that stimulate the thyroid gland (thyroid stimulating antibodies).
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 because of the inflammation.
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. Left untreated, however, hyperthyroidism places undue stress on the heart and many other organs.
Beta-blockerssuch as propranolol or metoprolol 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.
Methimazole 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 within 6 to 12 weeks. Larger doses of these drugs may work more quickly but increase the risk of side effects. Methimazole is usually preferred because propylthiouracil may damage the liver in young people. Pregnant women who take propylthiouracil or methimazole are closely monitored because these drugs cross the placenta and can cause goiter or hypothyroidism in the fetus. Carbimazole, a drug that is widely used in Europe, is converted into methimazole in the body.
Iodine,given by mouth, is sometimes used to treat hyperthyroidism. It is reserved for people 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. 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.
Drugs Used to Treat Hyperthyroidism
Surgery to remove part or all 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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