Hyperthyroidism is an excess of thyroid hormone resulting from overactivity of the thyroid gland. It speeds up processes in the body and may cause symptoms such as nervousness, tremor, sudden weight loss, rapid heartbeat and thyroid enlargement (goiter).

In some cases, hyperthyroidism also affects the eyes and the skin, particularly on the shins and feet. Potential complications of hyperthyroidism include heart problems and osteoporosis.

Several disorders can cause hyperthyroidism. They include:

• Graves' disease. An autoimmune disorder in which antibodies stimulate the thyroid to produce too much thyroid hormone.
  
  
• Hyperfunctioning thyroid nodules. Occurs when lumps in the thyroid, which are generally noncancerous, produce too much thyroid hormone.
  
  
• Thyroiditis. Inflammation and temporary destruction of the thyroid gland, which can allow excess hormones to leak into the bloodstream.

Diagnosing hyperthyroidism can be difficult because symptoms may mimic those of other conditions. A physical examination often reveals signs and symptoms such as eye problems or brittle hair. Thyroid blood tests aid in diagnosis.

Treatment options include radioactive iodine taken in pill or liquid form to shrink the thyroid gland. Antithyroid medications and surgery also may be used. Some therapies affect the thyroid gland so significantly that patients may develop hypothyroidism (underactive thyroid) and have to take hormonal supplements.

Hyperthyroidism is a condition in which overactivity of the thyroid gland causes too much thyroid hormone to build up in the bloodstream. As a result, processes in the body speed up. Left untreated, hyperthyroidism can have serious health consequences.

The thyroid gland sits just below the Adam's apple in the neck. It secretes hormones that regulate a person's metabolism, the physical and chemical processes necessary for the maintenance of life. Thyroid hormones help to:

• Control the rate at which the body uses fats and carbohydrates
  
• Maintain body temperature
  
• Influence heart rate
  
• Regulate the amount of calcium in the blood

A complex chain leads to hormone production in the thyroid. The hypothalamus in the brain signals the pituitary gland to make and release thyroid-stimulating hormone (TSH). TSH causes the release of the major thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Disorders that affect the thyroid have a crucial effect on the proper release of these hormones, which may alter a person's metabolism and potentially lead to significant health problems.

Hyperthyroidism occurs when a person’s thyroid produces too much thyroxine. This leads to a speeding up of metabolism that can result in many different symptoms, including enlargement of the gland (goiter) and sudden unexplained weight loss. In addition, some cases of hyperthyroidism cause the eyes to bulge beyond their normal socket. Tissues and muscles behind the eyes swell, a condition known as Graves' ophthalmopathy. Hyperthyroidism also can affect the skin, particularly on the shins and feet. Redness and swelling are the most common symptoms associated with the skin.

Several complications are associated with hyperthyroidism. Some patients may develop heart problems such as rapid heart rate, atrial fibrillation (heart rhythm disorder) and heart failure (inability of the heart to circulate enough blood to meet the body's needs). Hyperthyroidism also can lead to brittle bones (osteoporosis) and fractures, as excessive levels of thyroid hormone can prevent the body from incorporating calcium into the bones. According to recent research, thyroid disease may raise the risk of glaucoma, a leading cause of blindness.

Finally, people with hyperthyroidism are at increased risk for thyrotoxic crisis. This is also known as thyroid crisis or thyroid storm. When this occurs, patients may experience a sudden intensification of their symptoms, including fever, rapid pulse and delirium.

Hyperthyroidism occurs when the thyroid gland releases too much of the hormone thyroxine (T4). Many disorders are associated with this malfunction of hormone production. These disorders include:

• Graves' disease. The leading cause of hyperthyroidism, accounting for about 70 percent of all cases, according to the American Thyroid Association. Graves' disease is an autoimmune disorder, which means that the body's immune system sends antibodies that stimulate the thyroid to produce excess thyroxine. These antibodies also may attack the tissues behind the eyes and the skin on the lower legs over the shins. The cause of Graves' disease remains unknown, although a genetic predisposition is suspected.
  
  
• Hyperfunctioning thyroid nodules. Occurs when certain areas of the thyroid gland separate from the rest of the gland and produce masses, which are generally noncancerous, called adenomas. The adenomas may be big enough to enlarge the thyroid. They may sometimes produce excess thyroxine.
  
  
• Thyroiditis. Inflammation and temporary destruction of the thyroid gland, which can allow excess hormones to leak into the bloodstream. It can result from a viral infection or problem with the immune system. Thyroiditis may cause hyperthyroidism or hypothyroidism (too little thyroid hormones). Major types include Hashimoto's thyroiditis, subacute granulomatous thyroiditis and silent lymphocytic thyroiditis. Hashimoto's thyroiditis is generally a condition of hypothyroidism but may have a hyperthyroid phase. Most forms of thyroiditis are painless.
  
  Pregnancy can result in postpartum thyroiditis. About 5 to 10 percent of new mothers experience short-term hyperthyroidism, often followed by a few months of hypothyroidism, according to the American Association of Clinical Endocrinologists. Most of these women regain normal thyroid function, but some develop chronic hypothyroidism requiring lifelong treatment.

People with autoimmune disorders, such as type 1 diabetes, have increased risk of Graves' disease, Hashimoto's thyroiditis and other autoimmune conditions.

Other factors that can lead to hyperthyroidism include:

• Ingestion of large amounts of thyroid hormone or iodine.
  
• Tumors of the testes or ovaries.
  
• Thyroid cancer (in rare cases).
  
• Exposure to radioactive iodine. Researchers studying children who were exposed to radiation at the Nevada Test Site in the mid-20th century have found an increased risk of autoimmune thyroiditis and thyroid tumors.

Hyperthyroidism can affect both sexes and all ages, but most often affects women between the ages of 20 and 40. It develops in less than 1 percent of Americans, according to the American Association of Clinical Endocrinologists.

Patients with hyperthyroidism experience a significant acceleration of their metabolism. In many cases, this first appears as simple nervousness that many patients attribute to stress. Over time, other symptoms may emerge, including:

• Changes in bowel patterns. In particular, patients are more likely to have increased frequency of bowel movements.
  
  
• Changes to appearance. Patients may experience thinning of the skin and may develop fine, brittle hair.
  
  
• Enlarged thyroid gland. Also known as goiter, this can be felt or even seen as a swelling at the base of the neck.
  
  
• Irregular or rapid heartbeat. Patients may experience irregular heartbeat (arrhythmia) and palpitations. They also may experience rapid heartbeat of more than 100 beats per minute.
  
  
• Irritability. Patients sometimes experience anxiety attacks.
  
  
• Sudden unexplained weight loss. Patients often lose weight despite an appetite and food intake that remain normal or that increases (polyphagia).
  
  
• Sweating. Some patients also may experience increased sensitivity to heat.
  
  
• Tremor. Most often, this appears as a fine trembling in the hands or fingers.
  
  
• Irregular menstruation. Women may experience light or absent periods.

Patients also may experience difficulty sleeping, fatigue and muscle weakness. Symptoms are less likely to be evident in older patients. The use of beta blockers (antihypertensives used to treat high blood pressure and some heart conditions) can mask symptoms of hyperthyroidism.

Patients who experience the swelling behind the eyes known as Graves' ophthalmopathy may have dryness on the surface of the eye. Other symptoms include red or swollen eyes, excessive tearing or discomfort in the eyes, and any of the following:

• Blurry or double vision
  
• Inflammation
  
• Sensitivity to light
  
• Reduced eye movement

Diagnosing hyperthyroidism can be difficult because symptoms associated with the disorder often mimic those of other conditions. Diagnosis typically begins with the physician reviewing the patient's medical history and performing a physical examination.

The patient will be asked to swallow while the physician examines the thyroid gland for changes. The physician also looks for signs such as tremor in the fingers when they are extended, overactive reflexes, changes in the eyes and skin that is warm and moist. Changes in certain vital signs (pulse, rate of breathing) may indicate an increased heart rate. Blood pressure may be high, particularly systolic pressure (the top number in a blood pressure reading).

Thyroid blood tests also are used to diagnose hyperthyroidism. In most cases, levels of thyroid-stimulating hormone (TSH) are low while measures of thyroxine (T4) and triiodothyronine (T3) are high. Sometimes, the TSH can be low but the T4 and T3 are normal.

When blood testing reveals hyperthyroidism, other tests will be performed to pinpoint the cause of the overactive thyroid. During a radioactive iodine uptake test, the patient takes an oral dose of radioactive iodine. Because the thyroid uses iodine to make hormones, the iodine collects in the thyroid gland.

Patients are tested three and/or 24 hours after taking the iodine to see how much of the substance has been absorbed into the thyroid. If too much iodine is present, the thyroid gland likely is producing too much thyroxine, which indicates Graves' disease or hyperfunctioning nodules. If too little iodine is present, the patient may have thyroiditis.

Thyroid scans also can help determine the source of hyperthyroidism. A radioisotope is injected into the patient, who then lies on a table with the chin up and the neck extended backward. A special camera captures images of the thyroid on a computer screen.

There are various treatments available to treat patients with hyperthyroidism. A physician can help determine the best course of treatment based on a patient's condition and other factors.

Radioactive iodine can be taken in pill or liquid form to shrink the thyroid gland, reducing symptoms. Normally, thyroid cells take up iodine when creating thyroid hormone. When radioactive iodine is introduced, the thyroid cells take up this type of iodine as well, resulting in destruction of these cells and reduced production of thyroid hormone. More than 70 percent of adults with hyperthyroidism are treated with radioactive iodine, according to the American Thyroid Association. Among the hundreds of thousands of people who have been treated with radioactive iodine, there have been no reports of serious complications, according to the American Association of Clinical Endocrinologists.

There have been cases of patients who received radioactive iodine setting off radiation detectors at airports weeks after the treatment. Patients who get this treatment may wish to ask their physician to write an explanatory letter for security personnel.

Though this therapy often is effective, over time it shrinks the thyroid so significantly that patients eventually produce too little thyroid hormone (hypothyroidism). When this occurs, patients are required to take thyroid hormone replacement medicines for the rest of their lives.

Antithyroid medications also can prevent the gland from producing excess amounts of hormones. In some cases, medications may be effective for a period of time before a relapse of hyperthyroidism occurs. For example, between 20 and 30 percent of patients with Graves' disease who take these medications for up to 18 months will experience prolonged remission of their illness, according to the American Thyroid Association.

Side effects with these drugs are rare but may include allergic reaction, liver damage and a potentially dangerous reduction in white blood cell counts.

Beta blockers, a class of antihypertensive medications used to treat high blood pressure and heart conditions, can control symptoms such as rapid heart rate, tremors and nervousness. Possible side effects of beta blockers include dizziness, fatigue, insulin resistance, elevated cholesterol and sexual dysfunction. Beta blockers are typically discontinued when the hyperthyroidism is controlled by thyroid drugs, radioactive iodine or surgery.

Some patients may require thyroid surgery. This most often is recommended for patients who have large goiters that impair breathing ability or when other treatments fail to work. In these procedures, some or all (thyroidectomy) of the thyroid may be removed.

Thyroid surgery includes risk of damage to the vocal cords (which can cause hoarseness) and the parathyroid glands, which control the level of calcium in the blood. Damage to the parathyroid glands may require the patient to take medication to ensure that levels of calcium in the bloodstream remain normal. Surgery also may leave a scar on the neck.

Patients who have their thyroid removed or significantly reduced will be required to take thyroid hormone supplements for the rest of their lives.

A physician may prescribe exercise to help patients cope with fatigue and muscle weakness. Research has shown that physical activity can help people who are suffering fatigue to feel more energetic and less tired.

Patients diagnosed with Graves' ophthalmopathy may be able to treat mild symptoms with simple self-care techniques. In some cases, surgery or other treatments may be required.

Patients generally cannot prevent hyperthyroidism. However, various self-care techniques may be used to reduce symptoms. For example, patients who lose excessive amounts of weight due to their condition may benefit from a high-calorie, high-protein diet. They also can reduce the risk of osteoporosis and fractures by making sure they receive adequate levels of calcium and vitamin D in their diets.

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about hyperthyroidism:

1. What are the first signs that I may have hyperthyroidism?
   
   
2. How will you diagnose my hyperthyroidism?
   
   
3. How should I prepare for blood tests or imaging tests?
   
   
4. What is the likely source of my hyperthyroidism?
   
   
5. Do I have any of the conditions related to hyperthyroidism?
   
   
6. Do I have Graves' ophthalmopathy?
   
   
7. What are my treatment options? What are the pros and cons of these treatments?
   
   
8. How long will I need to take my antithyroid medication or radioactive iodine?
   
   
9. Can my treatment with radioactive iodine set off radiation detectors, such as at an airport? How long after my treatment is finished could this happen? Should I have a letter from you so I can inform security personnel of this side effect?
   
   
10. Will I need to take a thyroid supplement for the rest of my life?
    
    
11. What is my long-term prognosis?