Underactive Thyroid (Hypothyroidism)

Symptoms

Many symptoms of an underactive thyroid (hypothyroidism) are the same as those of other conditions, so it can easily be confused for something else.

Symptoms usually develop slowly and you may not realise you have a medical problem for several years.

Common symptoms include:

• tiredness
• being sensitive to cold
• weight gain
• constipation
• depression
• slow movements and thoughts
• muscle aches and weakness
• muscle cramps
• dry and scaly skin
• brittle hair and nails
• loss of libido (sex drive)
• pain, numbness and a tingling sensation in the hand and fingers (carpal tunnel syndrome)
• irregular periods or heavy periods

Elderly people with an underactive thyroid may develop memory problems and depression. Children may experience slower growth and development. Teenagers may start puberty earlier than normal.

If you have any of these symptoms, see a GP and ask to be tested for an underactive thyroid.

If an underactive thyroid is not treated

It's unlikely that you'd have many of the later symptoms of an underactive thyroid, because the condition is often identified before more serious symptoms appear.

Later symptoms of an underactive thyroid include:

• a low-pitched and hoarse voice
• a puffy-looking face
• thinned or partly missing eyebrows
• a slow heart rate
• hearing loss

• anaemia
  

Causes

An underactive thyroid (hypothyroidism) is when your thyroid gland does not produce enough of the hormone thyroxine (also called T4).

Most cases of an underactive thyroid are caused by the immune system attacking the thyroid gland and damaging it, or by damage that occurs as a result of treatments for thyroid cancer or an overactive thyroid.

Immune system

An underactive thyroid often occurs when the immune system, which usually fights infection, attacks the thyroid gland. This damages the thyroid, which means it's not able to make enough of the hormone thyroxine, leading to the symptoms of an underactive thyroid.

A condition called Hashimoto's disease is the most common type of autoimmune reaction that causes an underactive thyroid.

It's not clear what causes Hashimoto's disease, but it runs in families. It's also common in people with another immune system disorder, such as type 1 diabetes and vitiligo.

Previous thyroid treatment

An underactive thyroid can also occur as a side effect or complication of previous treatment to the thyroid gland, such as surgery or a treatment called radioactive iodine therapy.

These treatments are sometimes used for an overactive thyroid (where the thyroid gland produces too much hormone) or thyroid cancer.

Less common causes

Worldwide, a lack of dietary iodine is a common cause of an underactive thyroid, because the body needs iodine to make thyroxine.

Babies are sometimes born with an underactive thyroid because the thyroid gland does not develop properly in the womb. This is called congenital hypothyroidism and is uncommon. It's usually picked up during routine screening soon after birth.

A problem with the pituitary gland could lead to an underactive thyroid. The pituitary gland sits at the base of the brain and regulates the thyroid. Therefore, damage to the pituitary gland may lead to an underactive thyroid.

An underactive thyroid has also been linked to some viral infections or some medicines used to treat other conditions, such as:

• Lithium – a medicine sometimes used to treat certain mental health conditions, including depression and bipolar disorder
• Amiodarone – a medicine sometimes used to treat an irregular heartbeat (arrhythmia)
• Interferons – a class of medicine sometimes used to treat certain types of cancer and hepatitis C

Speak to a GP or specialist if you're concerned that a medicine you're taking may be affecting your thyroid hormone levels.

Diagnosis

It's very important that an underactive thyroid (hypothyroidism) is diagnosed as soon as possible.

Low levels of thyroid-producing hormones, such as triiodothyronine (T3) and thyroxine (T4), can change the way the body processes fat.

This can cause high cholesterol and atherosclerosis (clogging of the arteries), which can potentially lead to serious heart-related problems, such as angina and a heart attack. Therefore, you should see a GP and ask for a blood test if you repeatedly have symptoms of an underactive thyroid.

Thyroid function test

A blood test measuring your hormone levels is the only accurate way to find out whether there's a problem.

The test, called a thyroid function test, looks at levels of thyroid-stimulating hormone (TSH) and thyroxine (T4) in the blood. Doctors may refer to this as "free" T4 (FT4).

A high level of TSH and a low level of T4 in the blood could mean you have an underactive thyroid.

If your test results show raised TSH but normal T4, you may be at risk of developing an underactive thyroid in the future.

The GP may recommend that you have a repeat blood test every so often to see whether you eventually develop an underactive thyroid.

Blood tests are also sometimes used for other measurements, such as checking the level of a hormone called triiodothyronine (T3). However, this is not routinely offered.

Less commonly, a thyroid antibody test may be recommended after a thyroid function test. This is to help diagnose or rule out autoimmune thyroid conditions, such as Hashimoto's thyroiditis. A thyroid antibody test is only likely to be recommended if the GP suspects you have an autoimmune thyroid condition.

Referral

A GP may refer you to an endocrinologist (a specialist in hormone disorders) if you:

• are younger than 16
• are pregnant or trying to get pregnant
• have just given birth
• have another health condition, such as heart disease, which may complicate your medicine

• are taking a medicine known to cause a reduction in thyroid hormones, such as Amiodarone or Lithium
  

Treatment Options

An underactive thyroid (hypothyroidism) is usually treated by taking daily hormone replacement tablets called levothyroxine.

Levothyroxine replaces the thyroxine hormone, which your thyroid does not make enough of.

You'll initially have regular blood tests until the correct dose of levothyroxine is reached. This can take a little while to get right.

You may start on a low dose of levothyroxine, which may be increased gradually, depending on how your body responds. Some people start to feel better soon after beginning treatment, while others do not notice an improvement in their symptoms for several months.

Once you're taking the correct dose, you'll usually have a blood test once a year to monitor your hormone levels.

If blood tests suggest you may have an underactive thyroid, but you do not have any symptoms or they're very mild, you may not need any treatment. In these cases, the GP will usually monitor your hormone levels every few months and prescribe levothyroxine if you develop symptoms

Taking levothyroxine

If you're prescribed levothyroxine, you should take it at the same time every day. It's usually recommended that you take your tablet (or tablets) in the morning, although some people prefer to take them at night.

The effectiveness of the tablets can be altered by other medicines, supplements or foods, so they should be swallowed with water on an empty stomach, and you should avoid eating for 30 minutes afterwards.

If you forget to take a dose, take it as soon as you remember, if this is within a few hours of your usual time. If you do not remember until later than this, skip the dose and take the next dose at the usual time, unless advised otherwise by a doctor.

An underactive thyroid is a lifelong condition, so you'll usually need to take levothyroxine for the rest of your life.

If you're prescribed levothyroxine because you have an underactive thyroid, you're entitled to a medical exemption certificate. This means you do not have to pay for your prescriptions. See getting help with prescription costs for more information on this.

Side effects: Levothyroxine does not usually have any side effects, because the tablets simply replace a missing hormone. Side effects usually only occur if you're taking too much levothyroxine. This can cause problems including sweating, chest pain, headaches, diarrhoea and being sick.

Tell the doctor if you develop new symptoms while taking levothyroxine. You should also let them know if your symptoms get worse or do not improve.

Combination therapy 

sing levothyroxine and triiodothyronine (T3) together – is not routinely used because there's insufficient evidence to show it's better than using levothyroxine alone (monotherapy).

In most cases, suppressing thyroid-stimulating hormone (TSH) using high-dose thyroid replacement therapy should be avoided because it carries a risk of causing adverse side effects, such as atrial fibrillation (an irregular and abnormally fast heart rate), strokes, osteoporosis and fracture.

However, this type of treatment may sometimes be recommended in cases where a person has a history of thyroid cancer and there's a significant risk of it reoccurring.

Underactive thyroid and pregnancy

It's important for the health of you and your baby that an underactive thyroid is treated properly before you become pregnant.

Tell a GP if you're pregnant or trying to become pregnant and you have hypothyroidism. They may refer you to a specialist for treatment and monitoring during your pregnancy.