Hypothyroidism (underactive thyroid)
Hypothyroidism (underactive thyroid)
Hypothyroidism - Underactive Thyroid
Hypothyroidism means a reduced level of thyroid hormone (thyroxine). This can cause various symptoms, the most common being: tiredness, weight gain, constipation, aches, dry skin, lifeless hair and feeling cold. Treatment is usually easy by taking a tablet each day to replace the missing thyroxine. Treatment usually works well and symptoms usually go.
What is hypothyroidism?
Thyroxine is a hormone (body chemical) 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.
Hypothyroidism means that the thyroid gland does not make enough thyroxine. It is often called an underactive thyroid. This causes many of the body's functions to slow down.
(In contrast, if you have hyperthyroidism, you make too much thyroxine. This causes many of the body's functions to speed up.)
What are the symptoms of hypothyroidism?
Many symptoms can be caused by a low level of thyroxine. Basically, everything 'slows down'. Not all symptoms develop in all cases.
What are the possible complications of hypothyroidism?
If you have untreated hypothyroidism:You may have an increased risk of developing heart disease. This is because a low thyroxine level causes the blood lipids (cholesterol, etc) to rise.
Who gets hypothyroidism?
About 1 in 50 women, and about 1 in 1000 men develop hypothyroidism at some time in their life. It most commonly develops in adult women, and becomes more common with increasing age. However, it can occur at any age and can affect anyone.
What causes hypothyroidism?
Autoimmune thyroiditis - the common cause
The most common cause is due to an 'autoimmune disease' called autoimmune thyroiditis. The immune system normally makes antibodies to attack bacteria, viruses, and other 'germs'. If you have an autoimmune disease, the immune system makes antibodies against certain tissues of your body.
With autoimmune thyroiditis, you make antibodies that attach to your own thyroid gland which affect the glands function. The thyroid gland is then not able to make enough thyroxine, and hypothyroidism gradually develops. It is thought that something triggers the immune system to make antibodies against the thyroid. The 'trigger' is not known.
Autoimmune thyroiditis is more common than usual in people with:A family history of hypothyroidism caused by autoimmune thyroiditis.
Surgery or radioactive treatment to the thyroid gland
These are common causes of hypothyroidism in the UK due to increasing use of these treatments for other thyroid conditions.
Other causes of hypothyroidism are less common and include:
A blood test can diagnose hypothyroidism. 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:
Other tests are not usually necessary unless a rare cause of hypothyroidism is suspected. For example, tests of the pituitary gland may be done if both the TSH and T4 are low.
How is hypothyroidism treated?
The treatment is to take levothyroxine (thyroxine) tablets each day. This replaces the thyroxine which your thyroid gland is not making. Most people feel much better soon after starting treatment. Ideally, take the tablet on an empty stomach (before breakfast). This is because some foods rich in calcium or iron may interfere with the absorption of levothyroxine from the gut. (For the same reason, don't take levothyroxine tablets at the same time of day as calcium or iron tablets.)
What is the dose of levothyroxine?
Most adults need between 50 and 150 micrograms daily. A low dose is sometimes prescribed at first, especially in those over 60 or with heart problems, and is then gradually increased over a period of time. Blood tests are usually taken every 2-3 months, and the dose may be adjusted accordingly. The blood test measures TSH (see above). Once the blood TSH level is normal it means you are taking the correct amount of levothyroxine. It is then common practice to check the TSH blood level once a year. The dose may need adjustment in the early stages of pregnancy. Also, as you get into late middle age and older, you may need a reduced dose of levothyroxine.
Missed a tablet?
Everyone forgets to take their tablets from time to time. Don't worry as it is not dangerous to miss the odd forgotten levothyroxine tablet. You can take any missed doses as soon as you remember. However, you should try to take levothyroxine regularly each morning for maximum benefit.
How long is the treatment for?
For most people, treatment is for life. Occasionally, the disease process reverses. This is uncommon apart from the following:
Usually not. Levothyroxine tablets replace the body's natural hormone, so side-effects are uncommon. However, if you have angina, you may find that your angina pains become worse when you first start levothyroxine. Tell a doctor if this happens.
If you take too much levothyroxine it can lead to symptoms and problems of an over-active thyroid. For example, palpitations, diarrhoea, irritability, and sweating, and increases the risk of developing osteoporosis. This is why you need blood tests to check that you are taking the correct dose.
Other medicines may interfere with the action of levothyroxine. For example, carbamazepine, iron tablets, phenytoin, and rifampicin. If you start any of these medicines, or change the dose, then you may need to alter the dose of the levothyroxine. Your doctor will advise. Also, if you take warfarin, the dose may need to be altered if you have a change in your dose of levothyroxine.
If you have hypothyroidism, you are entitled to free prescriptions. This is for all your medicines, whether related to the hypothyroidism or not. Ask at your GP surgery for a form to fill in (form FP92A) to claim this benefit.
British Thyroid Foundation
PO Box 97, Clifford, Wetherby, West Yorkshire, LS23 6XD
Tel: Tel: 01423 709 707 and 01423 709 448 Web: www.btf-thyroid.org
Hypothyroidism, Clinical Knowledge Summaries (2007)
Boelaert K, Franklyn JA; Thyroid hormone in health and disease. J Endocrinol. 2005 Oct;187(1):1-15. [abstract]
UK guidelines for the use of thyroid function tests Association for Clinical Biochemistry, British Thyroid Association, British Thyroid Foundation. 2006
Comprehensive patient resources are available at www.patient.co.uk
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© EMIS and PiP 2008 Reviewed: 25 Jul 2008 DocID: 4272 Version: 39