Overactive thyroid

Overactive thyroid (also called hyperthyroidism) is a fairly common hormonal condition. It happens when there is too much thyroid hormone in the body.

Too much thyroid hormone can speed up the body's metabolism, and that can bring on a number of symptoms, such as:

• nervousness and anxiety
• hyperactivity (a person can't stay still and is full of nervous energy)
• unexplained or unplanned weight loss
• swelling of the thyroid gland, which causes a noticeable lump in the throat, known as a goitre

The symptoms differ from person to person. How severe they are, how often they come and which ones appear can all vary.

The thyroid gland sits in your neck. It makes hormones that pass into the bloodstream and control the body's growth and metabolism. These hormones are called thyroxine and triiodothyronine.

They affect things like heart rate and body temperature, and they help turn food into energy to keep your body going.

In an overactive thyroid, known as hyperthyroidism, the gland makes too much thyroxine or triiodothyronine, and this speeds up the body's metabolism.

There are several possible underlying causes. The most common is Graves' disease, where the body's immune system targets the thyroid gland and makes it produce too much of the thyroid hormones.

An overactive thyroid usually responds well to treatment, and most people are able to control their symptoms.

The 3 most widely used treatments for an overactive thyroid gland are:

• thionamides, a group of medicines, including carbimazole and methimazole, that stop the thyroid gland making too much thyroid hormone
• radioiodine treatment, which uses a radioactive substance called iodine to shrink the thyroid gland and so reduce its activity (the radiation in the iodine is a very low dose and does not pose a threat to health)
• surgery, which in a small number of cases may be needed to remove some or all of the thyroid gland, particularly if there is a large goitre

Beta-blockers may also be used sometimes. They can temporarily relieve many of the symptoms, though they don't target the thyroid gland itself.

It's common for treatment to leave the thyroid not producing enough hormones. This is called an underactive thyroid gland (hypothyroidism). But an underactive thyroid is not usually serious, and it is easily treated.

About 1 in 20 people with Graves' disease will also develop eye symptoms, such as:

• double vision
• sensitivity to light (photophobia)
• tearing (excess production of tears)

This is called Graves' ophthalmopathy. You should see a doctor who specialises in eye conditions (an ophthalmologist) for it.

A rarer and more serious complication is a sudden, severe flare-up of symptoms, known as a thyroid storm. It can be life-threatening, because it causes severe dehydration and heart problems.

An overactive thyroid gland is about 10 times more common in women than in men.

For most people, the symptoms begin somewhere between the ages of 20 and 40. They can start at any age though, childhood included.

The condition is seen most often in white and Asian people, and less often in African-Caribbean people.

If you have hyperthyroidism (an overactive thyroid), you may notice some of these symptoms:

• hyperactivity
• mood swings, such as anxiety, irritability and nervousness
• difficulty sleeping (insomnia)
• feeling tired all the time (fatigue)
• muscle weakness
• needing to poo or pee more often
• excess fats in your poo, which can make it greasy and hard to flush down the toilet (steatorrhoea)
• sensitivity to heat and excess sweating
• unexplained or unexpected weight loss, even though your appetite has increased (in a small number of cases, the increased appetite can lead to weight gain)
• very infrequent or light periods, or periods stopping altogether
• infertility
• loss of interest in sex

If you have diabetes, hyperthyroidism may make your diabetic symptoms, such as extreme thirst and tiredness, worse.

If you have hyperthyroidism (an overactive thyroid), you may notice some of these physical signs:

• a swelling in your neck caused by an enlarged thyroid gland (goitre)
• an irregular or unusually fast heart rate (palpitations)
• trembling or shaking (tremor)
• warm, moist skin
• redness on the palms of your hands
• nails loosening from their nail beds
• hives (urticaria)
• patchy hair loss (alopecia)
• twitching in your face and limbs

See a doctor if you have any of these symptoms. They may not be caused by an overactive thyroid gland, but they still need to be looked into further.

It can help to write down your symptoms before you go, because a list often makes it easier for the doctor to reach the correct diagnosis.

An overactive thyroid (hyperthyroidism) happens when your thyroid gland makes too much of the thyroid hormones thyroxine or triiodothyronine.

Several different conditions can cause the gland to overproduce these hormones.

Graves' disease is the most common cause of an overactive thyroid. It can run in families and can start at any age, though it is most common in women aged 20 to 40 years old. If you smoke, you are more likely to develop it.

Graves' disease is an autoimmune condition. That means the immune system mistakes something in the body for a toxic substance and attacks it. Here, the attack falls on the thyroid gland, and the gland then makes too much thyroid hormone.

Nobody knows what makes the immune system do this. As with many autoimmune conditions, a mix of genetic and environmental factors is thought to be involved.

Your eyes may also be affected if you have Graves' disease. You may feel discomfort and see double. This is called Graves' ophthalmopathy. Your eyes may bulge out or look more prominent than before.

For more on Graves' ophthalmopathy, read the section on complications of an overactive thyroid gland.

Lumps can sometimes form in the thyroid gland. These are called nodules. Nobody knows why they develop, but they are usually non-cancerous (benign).

Some nodules, though, contain abnormal thyroid tissue, and this upsets the normal production of thyroxine or triiodothyronine. The result is an overactive thyroid. Nodules with this kind of abnormal tissue are called toxic.

Toxic thyroid nodules account for about 1 in 20 cases of hyperthyroidism.

Your thyroid gland uses the iodine in the food you eat to make two thyroid hormones, thyroxine and triiodothyronine. Taking extra iodine in supplements, though, can push the gland to make too much thyroxine or triiodothyronine.

This is called iodine-induced hyperthyroidism, and you may also hear it called the Jod-Basedow phenomenon. It usually only happens if you already have nodules in your thyroid gland.

Amiodarone is a medicine known as an anti-arrhythmic. It helps to control an irregular heartbeat (atrial fibrillation). It contains iodine, so if you have non-toxic nodules in your thyroid gland, taking amiodarone can cause an overactive thyroid (hyperthyroidism).

Amiodarone can also cause a second type of hyperthyroidism, through a harmful effect on the thyroid tissue. This type is usually more severe and harder to treat. It's called amiodarone-induced hyperthyroidism.

Very rarely, an overactive thyroid can be caused by thyroid cancer that starts in the thyroid follicles. This happens when cancer cells in the thyroid gland begin to make thyroxine or triiodothyronine. Doctors also call it functioning thyroid cancer.

See a doctor if you think you may have an overactive thyroid gland (hyperthyroidism).

Your doctor will base the diagnosis on your symptoms and on blood tests that check how well your thyroid gland is working. These are called thyroid function tests.

Your doctor will take a sample of your blood and test it for the levels of:

• thyroid-stimulating hormone (TSH)
• thyroxine and triiodothyronine (the thyroid hormones)

TSH is made in the pituitary gland in your brain, and it controls how much thyroxine and triiodothyronine your body produces.

When the levels of thyroxine and triiodothyronine in your blood are normal, your pituitary gland releases a normal level of TSH. When thyroid hormone production becomes excessive, the pituitary gland stops releasing TSH. And when the level of thyroxine or triiodothyronine drops, the pituitary gland makes more TSH to boost it.

If you have an overactive thyroid, the thyroid function test will show that the TSH in your blood is consistently lower than normal. A low TSH level means your thyroid gland is overactive and likely to be making too much thyroid hormone. This is the first part of the thyroid function test.

Your doctor will then test your blood for thyroxine and triiodothyronine. If you have an overactive thyroid, the levels of both these hormones will be higher than normal.

Sometimes your tests show normal thyroid hormone levels but a low or suppressed level of TSH. This is called a subclinical overactive thyroid gland. If you're diagnosed with it, you may not need treatment.

In most cases the low TSH in your blood goes back to normal within a couple of months, and the subclinical hyperthyroidism clears up by itself. You will still need another thyroid function test, so your doctor can keep an eye on your condition.

If tests confirm an overactive thyroid gland, your doctor may send you for further tests to find the underlying cause.

One test that may be used is an isotope thyroid scan. You swallow a small amount of a radioactive substance (an isotope), usually technetium, as a capsule or a liquid. A scan then measures how much of the isotope your thyroid gland has absorbed.

If your thyroid absorbs a high amount, the underlying cause is likely to be either Graves' disease or thyroid nodules. If the amount is low, the cause could be one of these:

• swelling (inflammation) of the thyroid gland (thyroiditis), often caused by your immune system mistakenly attacking thyroid tissue or, less commonly, by infection
• having too much iodine in your diet
• in rare cases, thyroid cancer

If your doctor finds that you have an overactive thyroid gland (hyperthyroidism), they will send you to an endocrinologist, a specialist in hormonal conditions, who will plan your treatment.

Thionamides, such as carbimazole and propylthiouracil, are a common treatment for an overactive thyroid. These medicines stop your thyroid gland making too much thyroxine or triiodothyronine.

Thionamides work on the production of thyroid hormone, not on the levels already in your body. So you will need to take them for several weeks before you notice an improvement, usually between 4 to 8 weeks.

Once production of the hormones is under control, your specialist may slowly reduce your medicine. You may need to keep taking thionamides for a long time, until the condition is under control.

Around 1 in 20 people have side effects when they first start thionamides, such as:

• itchy skin rash
• joint pain

These side effects should pass once your body gets used to the medicine.

In rare cases (around 1 in 500), thionamides cause a sudden drop in white blood cells (agranulocytosis). This can leave you extremely vulnerable to infection.

The symptoms of agranulocytosis include:

• fever
• gum pain, swelling and bleeding
• sore throat
• mouth ulcers
• persistent cough
• shortness of breath

If you are taking thionamides and have any of these symptoms, phone your doctor immediately for advice and an urgent blood test. If you can't reach your doctor, phone the 16263 health line or your local out-of-hours service.

Beta-blockers, such as propranolol or atenolol, can ease some of the symptoms of an overactive thyroid, including tremor (shaking and trembling), rapid heartbeat and hyperactivity.

Your specialist may prescribe a beta-blocker while the condition is still being diagnosed, or until thionamide brings your thyroid gland under control. But beta-blockers are not suitable if you have asthma.

Beta-blockers can sometimes cause side effects, including:

• feeling sick
• feeling tired all the time (fatigue)
• cold hands and feet
• trouble sleeping, sometimes with nightmares

Radioiodine treatment is a form of radiotherapy that doctors use for most types of overactive thyroid. The radioactive iodine shrinks your thyroid gland, so it can make less thyroid hormone than before.

You take it either as a drink or as a capsule you swallow. The dose of radioactivity is very low and isn't harmful.

You can't have radioiodine treatment if you are pregnant or breastfeeding. It may also not be suitable if you have eye problems, such as double vision or prominent (bulging) eyes.

Women should avoid getting pregnant for at least 6 months after the treatment. Men should not father a child for at least 4 months after it.

Most people need only a single dose. If a second dose is needed, it is usually given 6 to 12 months after the first.

Your doctor may also give you a short course of thionamides a few weeks before the radioiodine treatment, because this can relieve symptoms more quickly.

Sometimes your doctor will recommend one particular treatment for an overactive thyroid, based on things like your age, your symptoms and how much extra thyroid hormone is in your blood. In other cases you may be offered a choice between a long-term course of thionamides and radioiodine treatment. Both have advantages and disadvantages.

Advantages of thionamides include:

• they are straightforward to take and you do not have to go to hospital to take them
• there is less risk of getting an underactive thyroid gland (hypothyroidism) as a result of treatment

Disadvantages of thionamides include:

• treatment may not be as successful as radioiodine treatment
• there is a higher risk of side effects

Advantages of radioiodine treatment include:

• treatment is usually very successful

Disadvantages of radioiodine treatment include:

• there is a higher chance of your thyroid gland becoming underactive as a result of treatment
• radioiodine treatment is usually not suitable for people with additional symptoms affecting their eyes (Graves' ophthalmopathy)
• women have to avoid getting pregnant for at least 6 months, and men should not father a child for at least 4 months after treatment

You should discuss the potential risks and benefits of both types of treatment with the specialist in charge of your care.

Surgery to remove all or part of the thyroid gland is called a total or partial thyroidectomy. For an overactive thyroid that keeps coming back, it is a permanent cure.

Your specialist may suggest surgery if your thyroid gland is badly swollen (a large goitre) and is causing problems in your neck.

Surgery may also be recommended in other situations:

• a person can't have radioiodine treatment because they are pregnant, and they are unable or unwilling to take thionamides
• a person has a severe form of Graves' ophthalmopathy
• the symptoms return (relapse) after an earlier course of thionamides that had worked

Doctors normally recommend removing the whole thyroid gland, because then there is no chance of a relapse.

The downside is that you will need to take medicine for the rest of your life to make up for the lack of a working thyroid gland. These are the same medicines used to treat an underactive thyroid gland.

An overactive thyroid (hyperthyroidism) can lead to several complications, especially if it isn't treated.

If you have Graves' disease, you may also have problems with your eyes. This is called Graves' ophthalmopathy, and it's thought to happen when the immune system mistakenly attacks the tissues of the eyes. It affects around 1 in 20 people with Graves' disease.

The symptoms of Graves' ophthalmopathy include:

• eyes feeling dry and gritty
• sensitivity to light (photophobia)
• excessive tearing
• double vision
• some loss of vision
• a feeling of pressure behind the eyes

In more severe cases, your eyes can bulge prominently from your eye sockets.

If you do develop Graves' ophthalmopathy, you will probably be referred to an eye specialist (ophthalmologist) for treatment.

The treatment options include:

• eyedrops to ease the symptoms
• sunglasses to protect the eyes against bright lights
• corticosteroids to reduce inflammation
• radiotherapy
• surgery

Some women are already pregnant when they are first told they have an overactive thyroid gland. Becoming pregnant can also bring the symptoms back, especially in a woman who has had Graves' disease.

Pregnant women with an overactive thyroid are at a higher risk of complications during pregnancy and birth, such as miscarriage and eclampsia. They are also more likely to go into labour early and to have a baby with a low birthweight.

Because of this, pregnant women will need specialist treatment. The condition should be managed with medicines that don't affect the baby, and this is likely to be a medicine called propylthiouracil.

Treatment for an overactive thyroid often swings the other way, and the thyroid gland ends up releasing hormone levels that are too low. This is called an underactive thyroid gland (hypothyroidism). Sometimes it's only a temporary side effect of treatment, but it can often be permanent.

Symptoms of an underactive thyroid gland include:

• being sensitive to cold
• weight gain
• constipation
• depression
• tiredness

Hypothyroidism is treated with medicines that help replicate the effects of the thyroid hormones.

An overactive thyroid that hasn't been diagnosed, or isn't well controlled, can lead to a rare but serious reaction called a thyroid storm. It affects around 1 in 100 people with an overactive thyroid gland.

A thyroid storm is a severe and sudden flare-up of symptoms. The body's metabolism goes into overdrive, often because of a trigger such as:

• infection
• pregnancy
• not taking your medicine as directed
• damage to the thyroid gland, such as a punch to the throat

The symptoms of a thyroid storm include:

• a very rapid heartbeat (over 140 beats a minute)
• fever (a temperature higher than 38C/100.4F)
• dehydration, with diarrhoea and vomiting
• jaundice, which is a yellow tinge to your skin and eyes
• severe agitation and confusion
• hallucinations, which means seeing or hearing things that are not real
• psychosis, which means being unable to tell the difference between reality and your imagination
• excessive sweating
• chest pain
• muscle weakness

A thyroid storm is a medical emergency. If you think you or someone in your care is having this complication, you need to phone 999 for an ambulance.