Overview
The thyroid is a small, butterfly shaped gland in the front of the neck. Its hormones set the pace at which the body works. In an overactive thyroid, also called hyperthyroidism or thyrotoxicosis, the gland makes more hormone than the body needs and everything speeds up.
It is far more common in women, and often begins in early or middle adult life. Most people do well with treatment, although the treatment itself can leave the thyroid underactive.
Symptoms
- Losing weight although appetite is good or increased
- A fast or irregular heartbeat, or palpitations
- Trembling of the hands
- Feeling nervous, irritable or anxious, and mood swings
- Difficulty sleeping
- Sweating and not tolerating heat
- Tiredness and muscle weakness
- A swelling in the front of the neck
- Lighter or irregular periods
In older people the picture can be quieter: loss of appetite, or withdrawing from company, rather than restlessness.
When to see a doctor
See a doctor if you have the symptoms above, if you notice a swelling in the neck, or if your eyes start to feel gritty or look more prominent. Tell your doctor if you are pregnant or planning a pregnancy, as some treatments are not suitable.
Causes
The commonest cause is Graves' disease, an autoimmune condition in which the immune system stimulates the thyroid to work too hard. Lumps in the gland, called nodules, can also produce extra hormone.
Other causes include inflammation of the gland (thyroiditis), which releases stored hormone, too much iodine, taking more thyroid hormone medicine than the body needs, and some medicines such as amiodarone.
Risk factors
- Being a woman
- A family history of thyroid disease
- Other autoimmune conditions, including type 1 diabetes and pernicious anaemia
- A recent pregnancy
- A high intake of iodine, including from some medicines
- Smoking, which particularly worsens the eye problems of Graves' disease
Complications
- An irregular heartbeat (), which can lead to blood clots, stroke and heart failure
- Thinning of the bones (osteoporosis)
- Thyroid eye disease, with gritty, painful or bulging eyes and, rarely, loss of vision
- Problems in pregnancy, including pre-eclampsia, miscarriage, premature birth and low birthweight
- Thyroid storm, a sudden and life threatening flare
Prevention
An overactive thyroid usually cannot be prevented, because most causes are autoimmune. Complications can be reduced by taking treatment as prescribed, keeping to the blood test schedule, and not smoking, which protects the eyes.
Diagnosis
Blood tests measure thyroid stimulating hormone () and the thyroid hormones T4 and T3. A low TSH with raised thyroid hormones points to an overactive thyroid. Antibody tests help show whether Graves' disease is the cause, and scans can show whether nodules or inflammation are responsible.
Treatment
Anti-thyroid medicines such as carbimazole or propylthiouracil reduce the amount of hormone the gland makes, and are usually taken for a year or two. Rarely they affect the body's ability to fight infection, so a sore throat, mouth ulcers or fever while taking them should be reported to a doctor at once.
Radioiodine is a drink or capsule that shrinks the overactive gland. Surgery to remove part or all of the thyroid is another option, particularly for a large goitre. Both often lead to an underactive thyroid afterwards, treated with a daily tablet.
Beta blockers are often added early on to settle the fast heartbeat, trembling and anxiety while the main treatment takes effect. Treatment in pregnancy needs specialist care, as some medicines can harm the baby.
Myths and facts
Things people often say about this. Open each one to see what is true.
Myth“An overactive thyroid is not so bad, because at least you lose weight.”What is true?
Fact
The weight loss comes from the whole body working too fast, and that puts real strain on it. Untreated, an overactive thyroid can cause an irregular heartbeat, blood clots, stroke, heart failure and thinning of the bones. It needs treating, not welcoming.
Myth“Thyroid problems only happen to women.”What is true?
Fact
An overactive thyroid is much more common in women, but men and older people get it too. In older adults the signs can be different, such as loss of appetite or withdrawing from others, and are sometimes mistaken for depression.
Myth“Once I feel normal again I can stop the tablets.”What is true?
Fact
Anti-thyroid medicines are usually taken for a year or two, and feeling well means the treatment is working. Stopping early lets the overactivity return. Not taking the medicine as prescribed is also one of the things that can trigger a thyroid storm, which is a medical emergency.
Myth“Bulging or sore eyes are a side effect of thyroid medicines.”What is true?
Fact
Eye changes are part of Graves' disease itself, caused by swelling of the tissues behind the eye. They can begin before, during or after treatment of the thyroid. Smoking makes them worse, and any sudden change in vision needs urgent assessment.
Questions to ask your doctor
Tick the ones you want answered and take them with you.
Common questions
Will I need to take medicine for life?
Not always. Anti-thyroid medicines are often given for a year or two, and some people stay well afterwards. If radioiodine or surgery is used, or if the overactivity returns, a daily thyroid hormone tablet is usually needed long term.
Is an overactive thyroid dangerous in pregnancy?
If it is not controlled it raises the chance of pre-eclampsia, miscarriage, premature birth and low birthweight. It can be managed safely, but the choice of medicine matters, so tell your doctor as early as possible if you are pregnant or planning to be.
Why have my eyes changed, and will they go back to normal?
Thyroid eye disease is caused by swelling of the tissues around the eye in Graves' disease. Many people have mild, gritty, watery eyes that settle, while some need specialist treatment. Not smoking helps, and any sudden change in vision should be checked urgently.
