What is it?
The thyroid is a small, butterfly-shaped gland with two lobes that sit either side of the windpipe, in men just below the Adam's apple. The thyroid gland produces hormones. Hormones are chemicals that act as your body’s messengers and travel through your blood sending a signal to different parts of your body. The hormones that the thyroid produces act on the cells in other parts of the body to increase the rate at which they use energy (metabolism). This is also called your metabolic rate. The thyroid gland produces 3 main hormones: Thyroxine (T4), triiodothyronine (T3) and calcitonin. The first two hormones affect your metabolism by increasing the metabolic rate (making you use more energy). T3 can be made in the thyroid from the breakdown of T4 and also by the same mechanism in other tissues in the body. The last hormone calcitonin contributes to controlling the levels of calcium and phosphorus in the blood which we need to keep our bones strong and healthy. It does not affect our metabolic rate.
Metabolism is important as the body needs fuel (energy) to keep all its parts working on a daily basis, for example to keep our heart beating and allow our lungs to move so that we can breathe. The rate at which we use this energy controls how quickly the cells and the tissues in our body work. If our body parts work too quickly or too slowly we may start to feel unwell. Because of this the production of the hormones from the thyroid gland need to be controlled. The brain controls the production of these hormones from thyroid gland via two areas called the hypothalamus and the pituitary gland which is above the roof of the mouth.
The hypothalamus first produces a chemical called thyrotrophin-releasing hormone (TRH). This travels to the pituitary gland which sits at the base of the hypothalamus and tells it to produce a chemical called thyroid-stimulating hormone (TSH). TSH is then released by the pituitary gland into the blood stream and travels to the thyroid gland to tell it to produce more thyroid hormones (T4 & T3). When you have enough thyroid hormone in your blood, the pituitary gland and the hypothalamus the production of TRH and TSH thus stopping the thyroid making the thyroid hormones. When the body needs more thyroid hormones the hypothalamus and pituitary secrete TRH and TSH again so that the thyroid gland is told to make more thyroid hormones. In this way the levels of T4 and T3 in your body are tightly regulated and your metabolic rate is controlled at the correct level in order for your body to function properly.
Another way the thyroid gland makes sure that we have the correct level of thyroid hormone is to store some of it inside the gland. Inside the thyroid, most of the T4 is stored attached to a protein called thyroglobulin. When more thyroid hormones are needed the thyroid not only makes more T4 but releases some of what is stored into the bloodstream. Once in the bloodstream, most of the T4 is attached to a protein called thyroxine-binding globulin (TBG). The tissues cannot absorb the T4 as well when it is attached to this protein. However when the T4 is needed by the tissues it is released from the protein so that the body can use it easily. T4 can also be converted to the more active T3 by the liver and many other tissues when needed. Most UK laboratories now measure T4 and T3 hormones in their active ‘free’ state which means that they are not bound to proteins. These tests are usually referred to as Free T4 (FT4) and Free T3 (FT3).
Hyperthyroidism - Hyperthyroidism means you have too much thyroid hormone. This makes your body use energy faster than it should and therefore some cells and tissues in your body work faster than they should do. Symptoms of hyperthyroidism are:
- Palpitations (fast or abnormal heart rate)
- Feeling anxious, nervous, irritable or emotional
- Anxiety & depression
- Difficulty sleeping
- Diarrhoea
- Feeling hot
- Weakness & fatigue
- Weight loss despite feeling hungry
- Tremor
- Hair loss
- Light or absent periods
- A swelling of your thyroid gland ( goitre)
- Eye problems such as blurred vision and eyes that appear enlarged if you have a type of hyperthyroidism called Graves disease
It is important to realise that most people will not have all the symptoms and in some people the symptoms may be very mild at first.
Graves disease
Hyperthyroidism (the overproduction of thyroid hormone) can be caused by different mechanisms. Graves’ disease is the most common cause of hyperthyroidism. In Graves’ disease the body produces antibodies that damage the thyroid and cause the release of thyroid hormones. Antibodies are produced to fight infections and any other harmful invaders that could damage the body. Sometimes, for reasons that aren't clear, the body produces antibodies that attack our own tissues. The production of antibodies against our own tissues leads to an autoimmune disease. In Graves’ disease, the thyroid gland, may become enlarged and swollen. An enlarged thyroid gland is called a goitre. These antibodies may also attack the eyes causing inflammation of the eye muscles. This can lead to problems with vision and also an enlargement of the eyes as the muscle behind the eyes becomes swollen.
Other causes of hyperthyroidism
Other causes of hyperthyroidism include inflammation of the thyroid gland which is known as thyroiditis. It generally occurs after a viral illness (which is known as subacute thyroiditis) or after a pregnancy (postpartum thyroiditis). Hyperthyroidism may also be caused by autoimmune diseases that are different to Graves disease, as well as by some medications e.g. amiodorone or lithium.
Less commonly hyperthyroidism is caused by a growth of part of the thyroid gland called a nodule. A nodule is simply a lump of tissue. One nodule may develop (e.g. toxic solitary adenoma) or occasionally multiple nodules may form (e.g. multinodular goitre).These nodules contain abnormal thyroid tissue so that the thyroid gland ends up producing more thyroid hormone than normal. They are usually non cancerous.
Treatment for hyperthyroidism
Treatment for hyperthyroidism often depends on the cause. However, options include having a single dose of radioactive iodine by mouth or by injection which gets taken up by the thyroid and kills some of the over productive cells. Other options include taking anti-thyroid tablets regularly (e.g. carbimazole) which suppresses the production of the thyroid hormone. These are usually taken for 1-2 years after which case the cause of the hyperthyroidism has normally resolved so the treatment can often be stopped. However a certain percentage of people may need to take carbimazole for the long term in order to keep their symptoms under control. Surgery to remove part of the thyroid is also an option and is often used in people with goitres that are large enought to put pressure on other areas such as the windpipe.
Occasionally some of these treatments may inadvertently stop too much of the thyroid gland from producing the thyroid hormones. This may then result in hypothyroidism and it may then be necessary to take thyroxine tablets to increase the thyroid hormone levels back to normal.
Hypothyroidism - Hypothyroidism means you have too little thyroid hormone. This makes your body use energy more slowly than it should and some parts of your body may work slower than normal. Hypothyroidism is common; in fact, you can have hypothyroidism for a number of years before it is recognised and treated. It is more common in women than men and it becomes more common as you get older. Symptoms of hypothyroidism include:
- Weight gain or fluid retention
- Depression
- Constipation
- Feeling cold
- Dry skin
- Thinning hair and brittle nails
- Tiredness
- Memory problems and poor concentration
- A slow heart rate
- Heavy /abnormal periods or infertility (not as common)
- Goitre (depending on the cause of the hypothyroidism)
Once again, sometimes only a few of these symptoms may be apparent in cases of hypothyroidism and the symptoms can often be mild.
Causes of Hypothyroidism
Hypothyroidism also has many different causes. Worldwide the most common cause is iodine deficiency as iodine is needed to make the thyroid hormones. However in the UK this is rare as our diet usually contains sufficient iodine. Vegetarians may have low iodine intake in their diet.
The commonest cause for hypothyroidism in the UK is an autoimmune disease called autoimmune thyroiditis. In this disease the thyroid gland is attacked by antibodies and can no longer make enough thyroxine. Hashimoto’s disease is the commonest form of autoimmune thyroiditis. In this form the thyroid gland also swells up and it is therefore associated with a goitre (swelling of the thyroid gland). Other rarer forms of autoimmune thyroiditis cause hypothyroidism.
Hypothyroidism may also occur secondary to treatment for an overactive thyroid (especially after surgery or radioactive treatment). In these cases too much of the thyroid tissue may have been damaged or removed and therefore the gland will not produce enough hormone. Medication (such as amiodarone or lithium) may also cause hypothyroidism by a variety of mechanisms In addition some children may be born with hypothyroidism if their thyroid gland has not developed properly. This is called congenital hypothyroidism. All babies are tested for this disease when they are born. Very rarely a problem with the pituitary gland in the brain may cause hypothyroidism. This is due to a lack of production from the pituitary of TSH so that the thyroid gets no signal to produce thyroid hormones when they are low. This is called ‘secondary hypothyroidism’.
Treatment for hypothyroidism is usually straightforward and involves taking tablets of thyroid hormone regularly. Treatment is usually life long as the condition is normally permanent.
Other Thyroid Diseases
Thyroid Cancer—There are 5 main types of thyroid cancer: papillary, follicular, medullary, anaplastic and thyroid lymphoma. Papillary and follicular cancers are slow growing and are usually straightforward to treat. Medullary cancer usually has a good outcome if it has not spread beyond the thyroid gland. Anaplastic thyroid cancer is the least common but it is the most aggressive form and spreads quickly. It can be difficult to treat. Lymphomas of the thyroid are not very common but are usually highly curable. Thyroid cancer may require different treatments such as surgery, chemotherapy, and radiotherapy depending on the type and how far the cancer has spread.
Solitary Thyroid Nodule—A solitary thyroid nodule is a small lump on the thyroid gland. By age 50 as many as 50% of the population will have a nodule somewhere in the thyroid. The overwhelming majority of these nodules are harmless. Some patients will have normal thyroid hormone levels. However some patients can have high or low thyroid hormone levels because of the nodules. Occasionally, thyroid nodules can be cancerous and need to be treated.
Goitre—A thyroid goitre is a visible enlargement of the thyroid gland. This rarely happens in developed countries, but is common in some areas in developing countries where there is little iodine in the diet. Iodine is needed to produce thyroid hormones so if iodineis in short supply the thyroid tries to compensate and grows in size. Other causes of a goitre involve an inflammation of the thyroid gland as occurs in Graves disease and Hashimoto's disease. Therefore goitres may be associated with producing too much or too little thyroid hormone. Sometimes however a patient with a goitre will have normal levels of thyroid hormones. Goitres can compress other structures of the neck such as the windpipe (trachea) and food pipe (oesophagus). This compression makes it difficult to breathe and swallow. The goitre has to be surgically removed.
Thyroiditis—Thyroiditis means that the thyroid gland is inflamed. This is usually due to autoimmune disease where the body produces antibodies that attack the thyroid gland. It may be also be due to a bacteria or a virus which act in the same was as antibodies in auto-immune disease to attack the thyroid gland. It can also occur after a pregnancy. Thyroiditis can cause hypothyroidism or hyperthyroidism and the symptoms can therefore vary. It can also cause fever and pain in the thyroid gland depending on the cause.What tests are used to detect a problem with the thyroid?
The first test your doctor will usually request to detect a problem with your thyroid gland is a TSH blood test. The TSH is usually low in hyperthyroidism and raised in hypothyroidism however this may not always be the case as other illnesses can also cause your TSH to be abnormal. Therefore if your TSH result is abnormal, the doctor will usually request a free T4 test (FT4) to confirm the diagnosis of thyroid disease.
In some laboratories the free T4 is processed at the same time as the TSH so the results may arrive together. If your thyroid is overactive the FT4 will usually be raised and the TSH low. If it is underactive the FT4 will usually be low and the TSH will be raised.
A free T3 test (FT3) may be requested as well but it is not as commonly tested as FT4. This is because a TSH and a FT4 result are usually sufficient enough to make a diagnosis. However in some cases of hyperthyroidism for example, FT3 may be increased but FT4 may be normal. This is not very common. However FT3 may be requested when investigating patients with symptoms of hyperthyroidism with a normal FT4 level.
- TSH – to test for hypothyroidism, and hyperthyroidism, to screen for secondary hypothyroidism (caused by the pituitary not secreting enough TSH), to screen newborns for hypothyroidism, and to monitor treatment with thyroid hormone tablets.
- Free T4 – to test for hypothyroidism and hyperthyroidism.
- Free T3 – to test for hyperthyroidism.
Additional tests that may be performed include:
- Thyroid antibodies - This tests for antibodies that are produced against the thyroid gland. Most commonly it tests for antibodies that attack a protein of the thyroid called thyroid peroxidase. This test is used in people with thyroid disease to help differentiate different types of thyroiditis and identify autoimmune thyroid conditions that may be causing the disease. It is also used to test for thyroid disease in people with an abnormal TSH but a normal thyroid hormone level. If these people have a positive thyroid antibody result it means that although they are producing the correct amount of thyroid hormone currently their thyroid gland is under attack by the antibodies. This may mean that their thyroid hormone levels may become abnormal in the future once the thyroid gland is no longer able to cope. This is often called subclinical hypothyroidism or subclinical hyperthyroidism. These patients often need to have their thyroid hormone levels monitored regularly.
- Calcitonin is a hormone that participates in calcium and phosphorusmetabolism. Calcitonin counteracts the actions of parathyroid hormone (PTH). Overproduction of calcitonin is a marker for medullary thyroid cancer. High calcitonin levels after surgery to remove the cancer may indicate recurrence. It may even be used on biopsy samples from suspicious lesions (e.g., lymph nodes that are swollen) to confirm metastases of the original cancer.
When are these laboratory tests requested?
Since one out of every 4,000 infants is born without a working thyroid gland, there is a UK screening programme for all newborn babies looking for hypothyroidism. This occurs approximately 1 week after birth and uses a drop of blood taken from a heel prick which is sent to the laboratory for a TSH test.
Thyroid function tests are also requested when a doctor notices that a patient has symptoms which can occur in thyroid disease. In hypothyroidism for instance a patient might show signs of fatigue, weight gain, increased sensitivity to cold, or skin dryness. In hyperthyroidism the signs might include fatigue, weight loss, increased sensitivity to heat, and nervousness. Tests are also requested in individuals who have a family history of thyroid disorders although they are not usually done unless someone has symptoms of thyroid disease or is unwell.
Non-Laboratory Tests
- Ultrasound – an imaging scan that allows doctors to look at a thyroid gland and determine whether a nodule is solid or fluid-filled. This can help determine what the cause of the nodule may be. Ultrasound can also help measure the size of the thyroid gland and tell whether it is enlarged or not.
- Thyroid Scans and uptake tests – a test that uses radioactive iodine or technetium to look for thyroid gland abnormalities and to evaluate thyroid function in different areas of the thyroid. The thyroid gland absorbs the radioactive substance from the blood stream and certain parts of the thyroid may take up more or less of the dye depending on how well the parts are working. An image of the gland is taken and you can see what areas have taken up more or less of the dye compared to others and can therefore see any areas of the thyroid which may be abnormal. It is very useful in investigating the nature of nodules and the possible causes of enlarged thyroid glands. Thyroid uptake tests are very similar to this however the scan may be repeated at different times over a 24-hour period.
- Biopsies – often a fine-needle biopsy, a procedure that involves inserting a needle into the thyroid and removing a small amount of tissue and/or fluid from a nodule or other area that the doctor wants to examine; an ultrasound is used to guide the needle into the correct position. You will need a general anaesthetic.
1. Are any thyroid diseases hereditary? Yes, Hashimoto’s thyroiditis and Graves’ disease may run in families. These are autoimmune diseases.
2. Are thyroid diseases more common in men or women? Hypothyroidism is 10 times more common in women.
3. Are certain people more likely to get thyroid disease? Yes apart from women and those with a family history, patients with other autoimmune diseases (e.g diabetes, pernicious anaemia, vitiligo) are more likely to develop thyroid disease. Patients with Down’s Syndrome and a condition called Turner’s syndrome are also more likely to get the disease.
4. Is thyroid disease permanent? Hyperthyroidism, depending on the cause often resolves in 1-2 years however some people may require anti-thyroid drugs for life. Hypothyroidism however is usually permanent and requires life-long treatment with thyroid hormone.
5. Do I have to pay for my thyroid treatment? People with hypothyroidism or conditions where they need to take extra thyroxine do not need to pay for prescriptions.
6. Can I still have a baby with a thyroid problem? You can still have a baby if you have a thyroid problem. However it is important for the baby for your thyroid levels to be adequately controlled during pregnancy and you should speak to a doctor if you are planning to become pregnant. Sometimes however thyroid problems can develop for the first time during a pregnancy. Thyroxine is safe to take in pregnancy as are anti-thyroid drugs.
7. How often is pregnancy complicated by a thyroid problem? Thyroid problems complicate 5% to 9% of all pregnancies. They can occur during pregnancy but can also occur after giving birth.
8. Are there any side effects from the medication? There are not usually any side effects from taking thyroxine. However if you take too much thyroxine you may develop symptoms of hyperthyroidism as the thyroid hormone levels in your blood will become too high. Therefore when you are on medication it is important to get your thyroid function checked regularly. If you are taking carbimazole you should not feel unwell as there are usually no ill-effects but the medication can cause your cells that fight infection to lower. This may mean that you end up with a fever, sore throat or other signs of infection. You should tell your doctor if any of these develop so a blood test can be done. Your thyroid hormone levels may also drop too low on anti-thyroid drugs such as carbimazole and therefore you may also develop symptoms of hypothyroidism. In this case you may need to take thyroxine to bring the levels back up. Therefore it also important if you are on treatment for hyperthyroidism to get your thyroid function monitored at regular intervals to ensure your that your thyroid hormone concentrations are in the correct range.