What is hypothyroidism?

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What is hypothyroidism?

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.

Hypothyroidism is also known as an underactive thyroid. It occurs

when the thyroid gland does not make enough thyroxine. 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 and pains, 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, carpal tunnel syndrome

(which causes pains and numbness in the hand), and memory loss or

confusion in the elderly.

If you have angina, you may find that your angina pains become more

frequent.

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.

Possible complications

If you have untreated hypothyroidism:

You have an increased risk of developing heart disease. This is

because a low thyroid 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.

With treatment, the outlook is excellent. Symptoms go, as do the

risk of 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.

Hypothyroidism is more common in

Women who have recently given birth.

Women with a family history of hypothyroidism caused by autoimmune

thyroiditis (see below).

People with Down's syndrome. It 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.

People with 's syndrome.

People who have had previous thyroid surgery.

People who have had previous radiotherapy to the head or neck for

any reason.

What causes hypothyroidism?

The common cause - autoimmune thyroiditis

The most common cause is due to an 'autoimmune disease' called

autoimmune thyroiditis (Hashimoto's disease). 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 which attack your own

thyroid gland. 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. People

with autoimmune thyroiditis have a small increased risk of

developing other autoimmune conditions including: pernicious

anaemia, type 1 diabetes, or 's disease. Autoimmune

thyroiditis also tends to run in some families. If you have this

condition, tell your children, particularly daughters, to look out

for the symptoms in their adult lives. Not all your children will

develop the hypothyroidism, but the risk is higher than average.

Other causes

Other causes are uncommon and include:

Surgery or radioactive treatment to the thyroid gland for other

conditions.

A side-effect to some medicines. (For example, amiodarone and

lithium.)

Other types of 'thyroiditis' (thyroid inflammation) caused by

infection or other rare conditions.

A pituitary gland problem is a rare cause. (The pituitary gland in

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).

Radiotherapy to the neck region for other conditions.

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 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 low, then the pituitary releases more TSH

to try and stimulate the thyroid gland even more. 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 suggest a

repeat blood test every year or so 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 thyroxine tablets each day. This replaces

the thyroxine which your thyroid gland is not making. Most people

feel much better quite quickly 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 thyroxine from the gut. (For the same reason, dont

take thyroxine tablets at the same time of day as calcium or iron

tablets.)

What is the dose of thyroxine?

Most adults need between 50 and 200 mcg daily. A low dose is

prescribed at first and is gradually increased over a period of

time. Blood tests are usually taken every now and then over several

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 getting the correct amount of thyroxine from the

tablets. It is then common practice to check the TSH blood level

once a year.

As you get into your 70s and 80s, you may need a reduced dose of

thyroxine. Also, if your weight changes by more than 1 stone (about

7 kg) due to dieting, weight gain, or pregnancy, you should have a

blood test sooner than the routine annual test as the dose may need

to be adjusted.

Missed a tablet?

Everyone forgets to take their tablets from time to time. Don't

worry as the odd forgotten thyroxine tablet will not make much

difference. However, you should try to take thyroxine regularly for

maximum benefit. Symptoms will gradually come back if you do not

take the tablets for several days or more.

How long is the treatment for?

For most people, treatment is for life. Occasionally the disease

process reverses. This is rare 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. About 1 in 20 women have thyroid imbalance for up to one

year after having a baby. Often this corrects itself. However,

afterwards it is wise to have a yearly blood test as there is an

increased chance of developing long-term hypothyroidism in the

future.

Are there any side-effects or problems from treatment?

Usually not. Thyroxine 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

thyroxine. Tell a doctor if this happens.

If you take too much thyroxine it can lead to symptoms of an over-

active thyroid, such as palpitations, diarrhoea, irritability, or

flushing. This is why the initial treatment dose is small and

gradually built up, and why you need blood tests to check that you

are taking the correct dose of thyroxine.

Other medicines may interfere with the action of thyroxine. For

example, carbamazepine, phenytoin, and rifampicin. If you start any

of these medicines, or change the dose, then you may need to alter

the dose of the thyroxine. 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 thyroxine.

In summary

Hypothyroidism is common.

Symptoms develop gradually. They may be confused with other

conditions.

Treatment with thyroxine tablets is usually easy and effective.

Treatment is usually for life.

Have a blood test once a year if you take thyroxine tablets.