Thyroid disease: what it is, symptoms, types and treatment

The thyroid produces hormones that affect things such as your heart rate and body temperature. The pituitary gland at the base of the brain controls it through thyroid-stimulating hormone (TSH), which is why a TSH blood test is usually the first check.

Thyroid disease is a broad term. The gland can make too little hormone, too much, or the normal amount but become swollen or lumpy. Each group has different causes and treatment, and several can overlap. For example, the same autoimmune process can cause Hashimoto's thyroiditis with a goitre, or Graves' disease with an overactive gland.

Symptoms depend on whether the thyroid is under- or overactive, or swollen. The NHS says underactive symptoms may be mild and not easy to notice, usually develop slowly and get worse over time. The British Thyroid Foundation adds that the changes can be so gradual that neither you nor your doctor notices until the condition is well advanced. Overactive symptoms, the NHS says, may develop gradually or suddenly and are unlikely to include all of those listed.

Many of these symptoms are common and have other causes, which is why a blood test is worth having rather than guessing.

Causes include Hashimoto's disease, surgery or radiotherapy around the neck, treatment for an overactive thyroid, some medicines and, rarely in the UK, not enough iodine in the diet. The British Thyroid Foundation lists lithium, amiodarone and some cancer immunotherapies among the medicines that can cause it.

Treatment is usually levothyroxine tablets to replace the missing hormone. The NHS says you will usually take them for the rest of your life, should be able to live a normal life, and will have regular blood tests to check you are on the right dose. The British Thyroid Foundation says that once the dose is stable you should have a blood test once a year.

The NHS says an untreated or under-treated underactive thyroid increases the risk of heart and bone problems, and that in very rare cases severe underactivity may lead to a life-threatening condition called myxoedema coma, which is more common in older people and is an emergency.

The NHS lists Graves' disease, thyroid nodules that make extra hormone, and some medicines containing iodine such as amiodarone among the causes, with thyroiditis, early or molar pregnancy and rarely thyroid cancer among others. The British Thyroid Foundation says Graves' disease has a strong genetic component, that stress may play a role, and that it is more common in people who smoke.

The NHS says the three main treatments are thionamide medicines (carbimazole or propylthiouracil), radioactive iodine treatment and surgery. Medicine is usually taken for 12 to 18 months, and the British Thyroid Foundation says a course of up to 18 months gives approximately a 30 to 50 per cent chance of cure, depending on goitre size and severity. After radioactive iodine the NHS says an underactive thyroid often follows.

Left untreated or poorly controlled, an overactive thyroid can cause eye problems (affecting around 1 in 4 people with Graves' disease, says the NHS), pregnancy complications and, rarely, a thyroid storm.

A goitre is a lump or swelling at the front of the neck caused by a swollen thyroid. The NHS says it is usually painless and not usually serious but should be checked by a GP. Causes include an overactive or underactive thyroid, harmless nodules, hormone changes during puberty, pregnancy or the menopause, thyroiditis, Graves' disease, too little iodine (rare in the UK) and, rarely, thyroid cancer.

The NHS says tests to find the cause may include blood tests, an ultrasound scan and a small needle sample (biopsy). Most goitres are small and cause no problems, and some need no treatment. If a goitre makes breathing or swallowing difficult, surgery to remove some or all of the thyroid may be used.

Thyroiditis means inflammation of the gland. The British Thyroid Foundation says the overactivity that goes with it is temporary and settles without specific treatment, with beta-blockers used to ease symptoms.

The first step is a thyroid function blood test measuring TSH and thyroxine (T4), sometimes with T3. The NHS says that for an overactive thyroid a low TSH with high T3 and/or T4 usually means you have it, and that what counts as normal varies with age and the laboratory method. The British Thyroid Foundation says an underactive thyroid typically shows a raised TSH with a low free T4.

Further tests depend on the picture. The NHS lists anti-thyroid antibody tests (usually found in Graves' disease), an ESR blood test to check for inflammation, and a thyroid scan to look for nodules. Some medicines, both prescribed and over the counter, can alter results, so tell the doctor about everything you take.

A slightly raised TSH with a normal thyroxine is called subclinical hypothyroidism. The British Thyroid Foundation says this may mean an increased risk of eventually developing full hypothyroidism, and regular thyroid function tests are advised.

Treatment depends on the type. For underactive thyroid, levothyroxine is best taken in the morning, with water, on an empty stomach at least half an hour before eating or drinking, according to the British Thyroid Foundation. It says calcium, iron, cholesterol-lowering drugs and multivitamins should be taken at least four hours apart. Always follow your own prescriber's advice.

For overactive thyroid you will usually be referred to an endocrinologist who plans treatment. The NHS says each option has benefits and drawbacks. It also warns that carbimazole can harm an unborn baby, so effective contraception is needed, and that a rare but serious side effect is a sudden drop in white blood cells; a high temperature, sore throat or persistent cough should be reported to a doctor immediately.

If you take thyroid medicine and plan a pregnancy, tell your GP early. The NHS says your levothyroxine dose is likely to need to change during pregnancy.

See a GP if you think you have symptoms of an underactive or overactive thyroid, or a lump or swelling in the neck.

The NHS says to call 999 or go to A&E if a goitre is making it hard to breathe or causing a wheezing noise when you breathe. A thyroid storm, a sudden flare-up of an overactive thyroid with rapid heartbeat, high temperature, severe agitation, confusion or loss of consciousness, is a medical emergency, and the NHS says to call 999.

Most thyroid disease is first found by a GP. The British Thyroid Foundation says an underactive thyroid is usually managed in primary care, with a doctor specialising in thyroid and other endocrine disorders involved if there are problems, and that the majority of people with hyperthyroidism should be assessed, at least initially, by a specialist.

Some people choose private endocrinology for faster scans or a second opinion. Ask which tests are being done and why, and discuss any change to prescribed medicines with your prescriber first.