Overproduction of thyroid hormones, causing many body functions to speed up

  • Most common between the ages of 20 and 50
  • More common in females
  • Sometimes runs in families
  • Lifestyle is not a significant factor

When the thyroid gland produces an excess of hormones, many of the body’s functions are stimulated by these hormones and speed up. This condition is known as hyperthyroidism and is one of the most common hormonal disorders. Hyperthyroidism is 7–10 times more common in women and usually develops between the ages of 20 and 50.

About 3 in 4 cases of the condition are due to Graves’ disease, an autoimmune disorder in which the immune system produces antibodies that attack the thyroid gland, resulting in overproduction of thyroid hormones. Graves’ disease tends to run in families and is thought to have a genetic basis. In rare cases, hyperthyroidism may be associated with other autoimmune disorders, in particular the skin disorder vitiligo and pernicious anaemia, a disorder of the blood (see Megaloblastic anaemia). In some cases, thyroid nodules that secrete hormones may be the cause of hyperthyroidism. Inflammation of the thyroid gland (see Thyroiditis) may temporarily produce symptoms of hyperthyroidism.

What are the symptoms?

In most cases, symptoms of hyperthyroidism develop gradually over several weeks and may include:

  • Weight loss despite increased appetite and food consumption.

  • Rapid heartbeat, which is sometimes also irregular.

  • Tremor (persistent trembling) affecting the hands.

  • Warm, moist skin as a result of excessive sweating.

  • Intolerance to heat.

  • Anxiety and insomnia.

  • Frequent bowel movements.

  • Swelling in the neck caused by an enlarged thyroid (see Goitre).

  • Muscle weakness.

  • In women, irregular menstruation.

People with hyperthyroidism caused by Graves’ disease may also have bulging eyes (see Exophthalmos).

How is it diagnosed?

If your doctor suspects that you have hyperthyroidism, he or she may arrange for a blood test to check for abnormally high levels of thyroid hormones and for antibodies that can attack the thyroid gland. Your doctor will also feel around your neck for lumps caused by general enlargement of the gland. If swelling is detected in this area, radionuclide scanning may be used to identify the cause of the hyperthyroidism.

What is the treatment?

Symptoms of hyperthyroidism can initially be relieved by beta-blocker drugs, which reduce tremor and anxiety but do not affect thyroid hormone levels. There are three main treatments aimed at reducing the production of thyroid hormones. The most common is antithyroid drugs (see Drugs for hyperthyroidism), which are used when hyper-thyroidism is due to Graves’ disease and work by suppressing production of thyroid hormones. These drugs need to be taken daily for 12–18 months, after which the thyroid gland often functions normally. Radioactive iodine may be the most effective treatment for hormone-secreting thyroid nodules. Treatment involves taking a capsule of radioactive iodine orally. The radioactive iodine is absorbed by the body and accumulates in the thyroid gland, destroying part of it. Surgical removal of part of the thyroid gland is an alternative treatment.

What is the prognosis?

Many people recover fully following treatment. However, hyperthyroidism may recur, particularly in people who have Graves’ disease. If the treatment involves surgery or radioactive iodine, the remaining part of the thyroid may not be able to produce sufficient hormones (see Hypothyroidism). It is therefore important for thyroid hormone levels to be monitored regularly after treatment so that hormone supplements can be given if needed.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

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