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Overactive thyroid

Hyperthyroidism occurs when the thyroid gland is too active and produces an excess of thyroid hormones. This makes the body's functions speed up and leads to symptoms such as shaking, weight loss and anxiety.

In the UK, about one in 500 men and one in 50 women will develop hyperthyroidism at some point in their lives in the UK.

  • About the thyroid gland
  • Symptoms
  • Causes
  • Diagnosis
  • Treatment
  • Further information
  • Sources
  • Related topics

About the thyroid gland

The thyroid gland is an endocrine gland. This means that it secretes hormones into your bloodstream. Hormones are chemicals produced by the body to help regulate how your cells and organs work. They are sometimes called chemical messengers.

Your thyroid gland is located in the neck in front of your windpipe. It is about 2cm wide and 4cm high.

What are the thyroid hormones?

The thyroid gland secretes two hormones: thyroxine (also called T4) and triiodothyronine (also called T3).

Together, these hormones regulate your body's metabolism. They control how quickly your body burns energy and how quickly reactions in your body happen.

Your rate of metabolism affects lots of things, such as how much you weigh and how much you sleep. Thyroxine and triiodothyronine speed up the body's metabolism, causing organs and processes in your body to work faster.

The production of the thyroid hormones is controlled by another hormone called thyroid stimulating hormone (TSH). This is made by an endocrine gland in the brain called the pituitary gland.

Symptoms

Hyperthyroidism has many different symptoms. In general, they relate to a speeding up of your body's metabolism. Some of the symptoms include:

  • feeling nervous, irritable or emotional
  • tremor (shaking)
  • sleeping poorly
  • being intolerant of heat and sweating more than usual
  • losing weight despite increased appetite (10% of people will gain weight)
  • feeling tired
  • muscle weakness
  • increased heart rate or palpitations
  • having infrequent periods or problems getting pregnant
  • having more frequent bowel movements or diarrhoea
  • shortness of breath, especially when exercising
  • loss of hair or finer hair than usual
  • swelling of the thyroid gland in the neck (goitre)
  • swollen/red eyes, or double vision (see Graves' disease)

Overactive and underactive thyroid

The opposite condition to hyperthyroidism is hypothyroidism. This happens when the thyroid is underactive and doesn't produce enough thyroid hormones. This slows down the body's metabolism, causing symptoms such as weight gain, tiredness and feeling cold.

For more information see Related topics.

Causes

Graves' disease

Graves' disease is the most common cause of hyperthyroidism in the UK. It is more likely to occur in women between the ages of 30 and 50. Graves' disease is an autoimmune disease. This means that it's caused by antibodies from your immune system attacking your body.

In Graves' disease, the antibodies mimic the activity of TSH, causing the thyroid gland to produce too much thyroid hormone, leading to hyperthyroid symptoms (see Symptoms).

About one in 20 people with Graves' disease also develop thyroid eye disease, also called Graves' ophthalmopathy. This is when the muscles in your eyes and surrounding tissue swell up, giving the eyes a bulging appearance. Your eyes may become red and puffy, and, occasionally, it can lead to double vision or limited eyeball movement. Thyroid eye disease doesn't always develop at exactly the same time as Graves' disease. It can occur before or after it as well.

You are more likely to get Graves' disease if you have close relatives affected by it.

Nodular thyroid disease

Small lumps or nodules within the thyroid gland also cause hyperthyroidism. Abnormal thyroid tissue within these nodules produces too much thyroid hormone. If one nodule forms, this is called toxic solitary adenoma. If more than one nodule forms, it is called a toxic multinodular goitre.

Other causes

There are other causes of hyperthyroidism, but these are rarer. For example, an inflamed thyroid gland (thyroiditis), which can be caused by a viral infection or an autoimmune attack, causes hyperthyroidism. Thyroiditis is also more likely if you are pregnant.

If you take too much medication that contains iodine, it may cause hyperthyroidism. An example is amiodarone, which is used to treat irregular heart beats.

Diagnosis

If you consistently have some or all of the symptoms given above you should talk to your GP about it. He or she will ask you about your symptoms, examine you, and may request some blood tests.

Blood tests

Hyperthyroidism can be diagnosed relatively easily with blood tests that check the levels of your thyroid hormones. The proportions of the different hormones can also help your doctor to decide what is causing your hyperthyroidism. Sometimes the presence of certain antibodies is also checked.

Other tests

If blood tests confirm that you have an overactive thyroid, your doctor will refer you to an endocrinologist (doctor who specialises in conditions that affect your hormones). He or she may do more tests to find out the cause of your hypothyroidism. Some of these tests are described below.

  • Iodine uptake test. A radioactive form of iodine is injected into your bloodstream; the thyroid uses this iodine to make thyroxine and triiodothyronine. The amount of iodine taken up is measured with a scanner. The dose of radioactivity is very low and isn't dangerous to you.
  • Ultrasound scanning. This measures the size of a goitre and whether it is pressing on neighbouring tissues in the neck.

Treatment

Your GP may give you drugs called beta-blockers to help control the symptoms of your hyperthyroidism. He or she may also refer you to an endocrinologist for treatment.

Treatment aims to bring your levels of thyroid hormones down to normal. This state is known as being euthyroid.

Medicines

Antithyroid drugs such as carbimazole and propylthiouracil suppress the production of your thyroid hormones and can control hyperthyroidism.

However, over time antithyroid drugs can lead to hypothyroidism, so you will need regular blood tests to monitor whether you are taking the correct dose.

Antithyroid drugs are prescribed for between 6 and 18 months. However, many people have a relapse and need longer term treatment.

Surgery

Another treatment is thyroidectomy. In this operation all or part of the thyroid gland is surgically removed.

Your doctor may suggest a thyroidectomy if you haven't responded to other treatments, if you are pregnant and can't take antithyroid drugs or if he or she thinks you may have thyroid cancer.

Thyroidectomy isn't a dangerous operation, but like any surgery, there are risks. These include bleeding, infection or damage to nearby nerves or other tissues. Talk to your doctor for more information.

Other treatments

Radioiodine

Radioiodine treatment can be used for most types of hyperthyroidism.

Radioiodine is iodine that has been made radioactive, similar to the iodine used for an iodine uptake scan (See Diagnosis). When the radioiodine is given in a tablet or drink form, it is taken up by your thyroid gland. As the radioactivity builds up it destroys some of the thyroid tissue. This allows the levels of your thyroid hormones to return to normal.

If just the right amount of radioiodine is given, it may be possible to destroy a portion of the thyroid gland so that it produces the correct level of thyroid hormones, but this is difficult.

Alternatively, you may be given a single large dose of radioiodine with the intention of stopping all thyroid activity. You can then take thyroxine tablets to prevent hypothyroidism from developing.

Radioiodine is not used in pregnant or breastfeeding women.

Treatment for thyroid eye disease

You may need treatment for the eye symptoms which can develop with Graves' disease (See Graves' disease). Options include eye drops, sunglasses or eye protectors for sleeping. Treatment for more severe eye problems include steroid tablets, radiation therapy or surgery. Talk to your doctor for more advice.

Further information

British Thyroid Foundation

British Thyroid Association

Sources

  • Hyperthyroidism Guidance. Clinical Knowledge Summaries. www.cks.library.nhs.uk, accessed 24 February 2007
  • Signs and Symptoms of Hyperthyroidism. British Thyroid Foundation. www.btf-thyroid.org, accessed 24 February 2007
  • Abraham P, Avenell A, Watson WA, Park CM, Bevan JS. Antithyroid drug regimen for treating Graves' hyperthyroidism. Cochrane Database of Systematic Reviews 2005, Issue 2
  • UK Guidelines for the Use of Thyroid Function Tests. The Association for Clinical Biochemistry, British Thyroid Association, British Thyroid Foundation, 2006. . www.british-thyroid-association.org, accessed 23 February 2007
  • Management of Hyperthyroidism and Hypothyroidism. British Thyroid Foundation. www.btf-thyroid.org, accessed 24 February 2007
  • Surgical Treatment of Diseases of the Thyroid Gland. The British Association of Thyroid and Endocrine Surgeons. www.baes.info, accessed 23 February 2007
  • Radioiodine Therapy. British Thyroid Foundation. www.btf-thyroid.org, accessed 24 February 2007

Related topics

Underactive thyroid