The thyroid gland is situated in the neck and consists of two lobes. It is not normally visible. The thyroid produces two hormones, triiodothyronine (T3) and thyroxine (T4). The thyroid maintains a large store of preformed hormone but also requires iodide (an iodine salt) in order to produce more supplies. Iodide is present naturally in water and food products and levels are usually sufficient to maintain an adequate intake. However, in some parts of the world far from the sea, the soil is deficient in iodine. People living in these areas may not have enough iodide in their diet to manufacture the correct level of hormones. In these instances public health measures, such as the addition of iodide to food products (eg, bread and salt), may have to be taken to ensure sufficient intake levels.
The thyroid hormones control the speed at which all cells in the body work (ie, the metabolism). Growth and development in babies and children are also controlled by these hormones, which are necessary for both physical growth and the development of the brain.
There are two main problems that can occur with the thyroid gland. It can become underactive causing decreased metabolism (hypothyroidism) or overactive causing increased metabolism (hyperthyroidism).
What is hyperthyroidism (overactive thyroid)?
The most common cause of an overactive thyroid gland is an auto-immune condition known as Graves' Disease. In people with this disease the immune system produces antibodies which overstimulate the thyroid gland. The thyroid gland then produces excess thyroid hormones, which can cause a range of symptoms. There is often a hereditary factor in Graves' Disease and females are much more likely to develop the disease than men. Graves' Disease is most common in women between the ages of 20 and 40 years.
Hashimoto's Disease is another auto-immune disease, which in the early stages produces symptoms similar to those seen in Graves' Disease.
What are the symptoms of hyperthyroidism?
The symptoms may develop slowly over a few months until it becomes clear that there is a problem. Symptoms include weight loss despite an increased appetite, nervousness, tremor, restlessness, palpitations and increased sweating. The eyes start to look larger and may bulge so that the person appears to be staring. The skin may become thinner and more delicate and women may notice that their periods become lighter or stop altogether. When the thyroid gland enlarges the neck may become noticeably swollen; when this happens it the swelling is referred to as a goitre. A blood test can confirm the overactivity of the thyroid gland.
What treatment is available?
Hyperthyroidism must always be treated. The increase in heart rate often seen in people with hyperthyroidism can lead to heart failure in severe cases, while young women with hyperthyroidism may be infertile so long as the condition remains untreated.
Hyperthyroidism may be treated with propylthiouracil or carbimazole, which is effective as long-term treatment and can also be given prior to surgery. Beta-blockers may also be prescribed to slow the heart rate. These do not cure the problem but can be given to keep the heart rate steady. Beta-blockers which may be prescribed include metoprolol and propranolol (eg, Bedranol® SR, Beta-Prograne®).
Other treatment options include surgery to remove part of the gland and radioactive iodine therapy. Your doctor will explain about these treatments if they are appropriate for you.
What is hypothyroidism (underactive thyroid)?
Thyroid hormone deficiency may occur for a number of reasons, including a lack of iodine in the diet. It may also occur following surgery for an overactive thyroid and in the later stages of Hashimoto's disease. Occasionally, drugs being taken for other conditions may interfere with the action of the thyroid gland. Examples of such drugs include amiodarone (taken for irregular heartbeats) and lithium (taken for certain mental disorders). Hypothyroidism can also occur temporarily in women after childbirth.
Myxoedema is the term used to describe a condition in which long-standing, untreated hypothyroidism exists.
What are the symptoms of hypothyroidism?
Underactivity of the thyroid causes changes which occur slowly and may go unrecognised for a long time. Symptoms include tiredness, lack of energy, intolerance of cold, dry skin, heavier periods and constipation. In later stages of untreated hypothyroidism (myxoedema) speech may become slow and slurred, mental disturbances may be apparent and unconsciousness may occur leading to a coma. A blood test can confirm underactivity of the thyroid.
What treatment is available?
For severe symptoms which have not been treated previously, such as in myxoedema, a drug called liothyronine can be given initially. Replacement therapy with levothyroxine (eg, Eltroxin®) is the standard treatment for hypothyroidism and for maintenance therapy following treatment with liothyronine. The correct dosage of levothyroxine for a person may take a long time to determine as regular blood tests and assessments may take place over several months. Levothyroxine is slow acting and the effects of the tablets are long term so it may be up to nine months before the person feels really well again. Some people can become addicted to their medication and may take more than the necessary dose. This can be dangerous and may have an unwanted effect on the heart. It can also cause osteoporosis which may lead to an increased tendency to break bones.
Further information available from:
British Thyroid Foundation
PO Box 97
Tel: 01423 709707
Fact sheet provided by MIMS
Date last reviewed: February 2008