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.
- Symptoms
that commonly occur include: tiredness, weight gain, constipation,
aches, feeling cold, dry skin, lifeless hair, fluid retention, mental
slowing, and depression.
- Less common symptoms include: a hoarse voice, irregular or heavy
menstrual periods in women, infertility, loss of sex drive, carpal
tunnel syndrome (which causes pains and numbness in the hand), and
memory loss or confusion in the elderly.
However, all these symptoms can be caused by other conditions,
and sometimes the diagnosis is not obvious. Symptoms usually develop
slowly, and gradually become worse over months or years as the level of
thyroxine in the body gradually falls.
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.
- If you are pregnant, you have an increased risk of developing some
pregnancy complications. For example: pre-eclampsia, anaemia, premature
labour, low birth weight, stillbirth, and serious bleeding after the
birth.
- Hypothyroid coma (myxoedema coma) is a very rare complication.
However, with treatment, the outlook is excellent. With
treatment, symptoms usually go, and you are very unlikely to develop
any complications.
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.
- Down's syndrome. Hypothyroidism develops in 1 in 3 people with
Down's syndrome before the age of 25 years. Symptoms of hypothyroidism
may be missed more easily in people with Down's syndrome. Therefore,
some doctors recommend that all people with Down's syndrome should have
an annual blood test to screen for hypothyroidism.
- Turner's syndrome. Again, an annual blood test to screen for hypothyroidism is usually advised for people with this condition.
- An enlarged thyroid gland (diffuse goitre).
- A past history of Graves' disease, or thyroiditis following childbirth.
- A personal or family history of other autoimmune disorders. For
example, vitiligo, pernicious anaemia, Addison's disease, Type 1
diabetes, premature ovarian failure, coeliac disease, Sjogren's
syndrome.
Some people with autoimmune thyroiditis also develop a swollen
thyroid gland (goitre). Autoimmune thyroiditis with a goitre is called
Hashimoto's disease. Also, people with autoimmune thyroiditis have a
small increased risk of developing other autoimmune conditions such as
vitiligo, pernicious anaemia, etc.
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
Other causes of hypothyroidism are less common and include:
- Worldwide, iodine deficiency is the most common cause of
hypothyroidism but it is a rare cause in the UK. (Your body needs
iodine to make thyroxine. However, it is rare for a diet in western
countries to lack sufficient iodine.)
- A side-effect to some medicines. For example, amiodarone and lithium.
- Other types of 'thyroiditis' (thyroid inflammation) caused by various rare conditions.
- A pituitary gland problem is a rare cause. The pituitary gland that
lies just under the brain makes a hormone called thyroid stimulating
hormone (TSH). This stimulates the thyroid gland to make thyroxine. If
the pituitary does not make TSH, then the thyroid cannot make enough
thyroxine.
- Some children are born with an underactive thyroid gland (congenital hypothyroidism).
How is hypothyroidism diagnosed?
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:
-
Thyroid-stimulating hormone (TSH).
This hormone is made in the pituitary gland. It is released into the
bloodstream. It stimulates the thyroid gland to make thyroxine. If the
level of thyroxine in the blood is low, then the pituitary releases
more TSH to try and stimulate the thyroid gland to make more thyroxine.
Therefore, a raised level of TSH means the thyroid gland is underactive
and is not making enough thyroxine.
-
Thyroxine (T4). A low level of T4 confirms hypothyroidism.
Note: some people have a raised TSH but have a normal T4. This
means that you are making enough thyroxine but the thyroid gland is
needing extra 'stimulation' from TSH to make the required amount of
thyroxine. In this situation you have an increased risk of developing
hypothyroidism in the future. Your doctor may advise a repeat blood
test every so often to see if you do eventually develop hypothyroidism.
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:
-
Children.
Sometimes hypothyroidism is a temporary condition in older children.
(This is not so for children who are born with an underactive thyroid.)
-
Pregnancy. Some women develop thyroid imbalance after having
a baby. If it occurs, it typically happens about three to six months
after the birth. Often this lasts just a few months and corrects
itself. Treatment is needed only in a small number of cases. However,
afterwards it is wise to have a yearly blood test as there is an
increased risk of developing autoimmune thyroiditis and long-term
hypothyroidism in the future.
Are there any side-effects or problems from treatment?
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.
Free prescriptions
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.
In summary
- Hypothyroidism is common.
- Symptoms develop gradually. They may be confused with other conditions.
- Treatment with levothyroxine tablets is usually easy and effective.
- Treatment is usually for life.
- Have a blood test once a year if you take levothyroxine tablets once your dose has become stabilised.
Disclaimer: This article is for information only and should not
be used for the diagnosis or treatment of medical conditions. EMIS and
PiP have used all reasonable care in compiling the information but make
no warranty as to its accuracy. Consult a doctor or other health care
professional for diagnosis and treatment of medical conditions.
© EMIS and PiP 2008 Reviewed: 25 Jul 2008
