Hyperthyroidism (Overactive Thyroid)

What is hyperthyroidism?

Thyroxine is a body chemical (hormone) made by the thyroid gland in the neck. It is carried round the body in the bloodstream. It helps to keep the body's functions (the metabolism) working at the correct pace. Many cells and tissues in the body need thyroxine to keep them going correctly.

Hyperthyroidism is also known as thyrotoxicosis or an overactive thyroid. It occurs when the thyroid gland makes too much thyroxine. This causes many of the body's functions to speed up. (In contrast, if you have hypothyroidism, you make too little thyroxine. This causes many of the body's functions to slow down.)

What are the symptoms of hyperthyroidism?

• Being restless, nervous, emotional, irritable, sleeping poorly, and 'always on the go'.
• Tremor of the hands.
• Losing weight despite an increased appetite.
• Palpitations.
• Sweating and a dislike of heat.
• Diarrhoea or needing to go to the toilet to pass stools (faeces) more often than normal.
• Shortness of breath.
• Skin problems such as hair thinning and itch.
• Menstrual changes - often the periods become very light or infrequent.
• Increased thirst.
• Tiredness and muscle weakness may be a feature.
• A swelling of the thyroid gland in the neck (goitre) may occur.
• Eye problems (if you have Graves' disease. See below.)

Most people with hyperthyroidism do not have all the symptoms, but a combination of two or more is common. Symptoms usually develop slowly over several weeks. All the symptoms can be caused by other problems, and so the diagnosis may not be obvious at first. Symptoms may be mild to start with, but become worse as the level of thyroxine in the blood gradually rises.

Possible complications
If you have untreated hyperthyroidism

• You have an increased risk of developing heart problems such as atrial fibrillation (an abnormal heart rhythm), cardiomyopathy (a weakened heart), angina, and heart failure.
• If you are pregnant, you have an increased risk of developing some pregnancy complications. For example: miscarriage, eclampsia, premature labour, low birth weight, stillbirth, and possibly congenital abnormality.
• You have an increased risk of developing osteoporosis.

With treatment, the outlook is good. Most of the symptoms and risks of complications go with successful treatment.

Who gets hyperthyroidism?

About 2 in 100 women, and 2 in 1000 men, develop hyperthyroidism at some stage of their life.

Graves' disease
Graves' disease is the commonest cause. It can occur at any age, but is most common in women aged 20 to 40. It can affect anyone, but there is often a family history of the condition.

Graves' disease is an autoimmune disease. The immune system normally makes antibodies to attack bacteria, viruses, and other 'bugs'. In autoimmune diseases, the immune system makes antibodies against tissues of the body. If you have Graves' disease, you make antibodies that attach to the thyroid gland. These stimulate the thyroid to make lots of thyroxine. It is thought that something triggers the immune system to make these antibodies. The 'trigger' is not known.

In Graves' disease the thyroid gland commonly enlarges which causes a swelling in the neck (goitre). The eyes are also commonly affected. Your eyes may seem to be pushed forward and look more prominent (proptosis). You may have discomfort and watering of the eyes. Problems with eye muscles may lead to double vision. It is not clear why eye symptoms occur in Graves' disease. They may be due to the antibodies affecting the tissues around the eye.

Thyroid nodules
This is a less common cause of hyperthyroidism. Thyroid nodules are lumps which can develop in the thyroid gland. It is not clear why they develop. They are usually benign (non-cancerous) but contain abnormal thyroid tissue. The abnormal thyroid tissue in the thyroid nodules does not respond to the normal controlling system which ensures that you make just the right amount of thyroxine. Therefore, if you have a thyroid nodule, you may make more than normal amounts of thyroxine.

• Sometimes only one nodule forms. This is called a 'toxic solitary adenoma'. This most commonly occurs in people aged between 30 and 50.
• The thyroid may become generally lumpy or nodular. This most commonly occurs in older people, and is called a 'toxic multi-nodular goitre'.

Other causes
There are several other rare causes of hyperthyroidism.

How is hyperthyroidism diagnosed?

A blood test can diagnose hyperthyroidism. A normal blood test will also rule it out if symptoms suggest that it may be a possible diagnosis. One or both of the following may be measured:

• Thyroid-stimulating hormone (TSH). This hormone is made in the pituitary gland in the brain. It is released into the bloodstream. It stimulates the thyroid gland to make thyroxine. If the level of thyroxine in the blood is high, then the pituitary releases less TSH. Therefore, a low level of TSH means the thyroid gland is overactive and is making too much thyroxine.
• Thyroxine (T4). A high level of T4 confirms hyperthyroidism.

Other tests are sometimes done to clarify the cause. For example, an ultrasound scan of the thyroid or a thyroid scan may be done if you have a nodular goitre. Other blood tests may be done if a rare cause is suspected.

What are the treatments for hyperthyroidism?

The main aim of treatment is to reduce the level of thyroxine to normal. Other problems such as a large goitre (thyroid swelling) or associated eye problems may also need treatment. Factors such as the underlying cause of the problem, your age, and the size of any goitre are taken into account to decide on the best treatment plan. Treatment options include the following.

Medicines - usually carbimazole
Medicines can reduce the amount of thyroxine that you make by the overactive thyroid gland. The most common medicine used in the UK is carbimazole. Carbimazole does not affect the thyroxine which is already made and stored, but reduces further production. Therefore, it may take 4 to 8 weeks of treatment for your thyroxine level to come down to normal.

The dose of carbimazole that is needed to keep the thyroxine level normal varies from person to person. Carbimazole is usually taken for 12-18 months at first. After this, in about half of cases, the condition will have settled down and the carbimazole can be stopped. If the condition flares up again some time in the future, a further course may be needed. In about half of cases, carbimazole needs to be continued long-term to control symptoms. A different treatment may then be a better option if you do not want to take carbimazole long-term.

Warning: carbimazole can, rarely, affect the white blood cells which fight infection. If you develop a fever, sore throat, mouth ulcers, or other symptoms of infection whilst you are taking carbimazole, stop taking the tablets immediately and see a doctor urgently for a blood test.

Radio-iodine
This involves taking a drink, or swallowing a capsule, which contains radioactive iodine. The main use of iodine in the body is to make thyroxine. Therefore, the radioactive iodine builds up in the thyroid gland. As the radioactivity is concentrated in the thyroid gland, it destroys some thyroid tissue which reduces the amount of thyroxine that you make. The dose of radioactivity to the rest of the body is very low and is not dangerous.

Thyroid replacement therapy
It can be difficult for a doctor to judge just the right dose of carbimazole, or just the right amount of radio-iodine, to give in each case. Too much treatment may make the thyroxine level go too low. Not enough treatment means the level remains higher than normal. Regular blood tests are needed to check on the thyroxine level.

One option is to deliberately take a high dose of carbimazole each day, or to take a one-off high dose of radio-iodine. This will stop your thyroid gland making any thyroxine. But, you can take a daily dose of thyroxine tablets to keep your blood level of thyroxine normal. This 'over-treatment' and then taking replacement thyroxine ('block and replace') is a popular option.

Surgery
This involves removing part of the thyroid gland. It may be a good option if you have a large goitre (thyroid swelling) which is causing problems in the neck. If too much of the thyroid is removed it is not usually a problem as you can take thyroxine tablets to keep the thyroxine level normal. It is usually a safe operation, although as with all operations there is a small risk.

Treatment for eye problems
You may need to see an eye specialist if you develop the eye problems of Graves' disease. Relatively minor symptoms affect the eyes in about half of people with Graves' disease. Measures such as artificial tears, sunglasses, and eye protectors whilst you sleep may be sufficient to help.

However, about 1 in 20 people with Graves' disease have severe eye changes. Treatment can then be more difficult and may include surgery, radiation treatment, or steroid tablets.

Beta-blocker medicines
Some people take a beta-blocker medicine (for example, propranolol, atenolol, etc) for a few weeks whilst the level of thyroxine is reduced gradually by one of the above treatments. Beta-blockers can block some of the effects of a high level of thyroxine. In particular they help to reduce the symptoms of tremor, palpitations, sweating, agitation, and anxiety.

Regular checks are recommended, even after you finish a successful treatment. A yearly blood test may be advised. This is because some people become hyperthyroid again sometime in the future. Others who have been treated successfully develop an underactive thyroid in the future. If this occurs it can usually be treated easily with thyroxine tablets.

In summary

• Hyperthyroidism can be caused by several diseases. Graves' disease is the most common.
• Various symptoms may gradually develop.
• Treatment options include: medicines, radio-iodine, and surgery.
• Over-treatment, and then replacement with thyroxine tablets is another option.
• Beta-blockers can ease some symptoms caused by a high level of thyroxine.
• Long term follow up is advised, even after successful treatment.

British Thyroid Foundation
PO Box 97, Clifford, Wetherby, West Yorkshire, LS23 6XD
Tel: 01423 709 707    Web: www.btf-thyroid.org

Thyroid Eye Disease (TED) Charitable Trust
PO BOX 2954, Calne, Wiltshire, SN11 8WR
Tel: 0844 800 8133    Web: www.tedct.co.uk

© EMIS and PIP 2006   Updated: November 2006   PRODIGY Validated