Overactive thyroid (hyperthyroidism)

Published by Bupa's Health Information Team, April 2010.

This factsheet is for people who have an overactive thyroid (hyperthyroidism), or who would like information about it.

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

About hyperthyroidism

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

Your thyroid gland is in your neck, in front of your windpipe. It's about 2cm wide and 4cm high.

Your thyroid gland makes two hormones: thyroxine (also called T4) and triiodothyronine (also called T3). Together, these hormones regulate your body's growth and metabolism. Your metabolism is 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.

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

What is hyperthyroidism?

Hyperthyroidism is when your thyroid gland is overactive and produces excess thyroid hormones. This speeds up your body's metabolism, meaning that organs and processes in your body work faster.

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

Symptoms of hyperthyroidism

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

• feeling nervous, irritable or emotional
• tremor (shaking)
• sleeping poorly
• being intolerant of heat and sweating more than usual
• losing weight despite having an increased appetite (although around one in 10 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 your thyroid gland (goitre)
• swollen/red eyes, or double vision

If you have some, or all, of these symptoms, see your GP.

Causes of hyperthyroidism

Graves' disease

Graves' disease is the most common cause of hyperthyroidism in the UK. It's 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 your thyroid gland to produce too much thyroid hormone, leading to the symptoms of hyperthyroidism.

About one in 25 people with Graves' disease also develop thyroid eye disease, called Graves' ophthalmopathy. This is when the muscles in your eyes and the surrounding tissue swell up, giving your eyes a bulging appearance. Your eyes may become red and puffy, and, occasionally, it can lead to double vision or limited movement of your eyeball. Thyroid eye disease doesn't always develop at exactly the same time as Graves' disease. It can occur before or after it as well.

Graves' disease is most common in women between the ages of 20 and 40. You're more likely to get Graves' disease if you have close relatives who are affected by it.

Nodular thyroid disease

Small lumps or nodules within your thyroid gland can cause hyperthyroidism, when 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's called a toxic multinodular goitre.

Other causes

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

If you take too much of a medicine that contains iodine, it may cause hyperthyroidism as your thyroid gland uses iodine to produce thyroid hormones. An example is the medicine amiodarone, which is used to treat irregular heart beats.

Diagnosis of hyperthyroidism

Your GP will ask you about your symptoms, examine you, and you may need to have a blood test.

Hyperthyroidism can be diagnosed 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 (proteins produced by your immune system) is also checked.

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

• Radioisotope scan (also called a radionuclide scan). A small amount of a radioactive substance, either iodine or technetium, is injected into your blood. The dose of radioactivity is low and isn't dangerous to you. Your doctor will pass a scanner over your neck, which allows overactive areas of your thyroid to be detected.
  
• Ultrasound scan. This is used to measure the size of a goitre and whether it's pressing on surrounding tissues in your neck.
  

Treatment of hyperthyroidism

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

Medicines

Your doctor may prescribe anti-thyroid medicines such as carbimazole and propylthiouracil, to reduce the production of thyroid hormones. However, over time anti-thyroid medicines can lead to hypothyroidism (an underactive thyroid), so you will need regular blood tests to monitor whether you are taking the correct dose.

Antithyroid medicines are usually prescribed for 12 to 18 months. However, many people need more long-term treatment.

Alternatively, your doctor may prescribe you medicines called beta-blockers to help control the symptoms of hyperthyroidism, but these don't treat the underlying problem.

Non-surgical treatments

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. You will be given radioiodine in a tablet or drink form, and it is taken up by your thyroid gland. As the radioactivity builds up it destroys some of your thyroid tissue. This allows the levels of your thyroid hormones to return to normal.

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

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

Radioiodine is not suitable if you're pregnant or breastfeeding.

Surgery

Another treatment option is a thyroidectomy. This is an operation to remove all or part of your thyroid gland. Your doctor may suggest a thyroidectomy if you haven't responded to other treatments, if you're pregnant and can't take anti-thyroid medicines or if he or she thinks you may have thyroid cancer. After the surgery, you may need to take thyroxine replacement medicines every day for the rest of your life.

Treatment for thyroid eye disease

You may need treatment for thyroid eye disease, which can develop if you have Graves' disease. You may need to use eye drops, wear sunglasses and use extra pillows to raise your head at night to reduce the swelling. Treatments for more severe eye symptoms include steroid medicines, radiation therapy or surgery. Talk to your doctor for more advice.

For answers to frequently asked questions on this topic, see Common questions.

For sources and links to further information, see Resources.