Hypothyroidism

Reviewed by Dr Dan Rutherford, GP

What is hypothyroidism?

The thyroid gland, located in the lower front of the neck, produces hormones that are extremely important for the regulation of the body's metabolism.

When the thyroid gland is unable to produce sufficient amounts of these hormones - thyroxine (T4) and tri-iodothyronine (T3) - then a large number of problems arise in all of the body's systems due to the decrease in the body's metabolism.

Hypothyroidism is more common among elderly people, especially women, and affects 1.5 to 2 per cent of people over the age of 60 years. However, the condition also occurs in younger patients.

What causes hypothyroidism?

The main causes of hypothyroidism are:

chronic autoimmune inflammation of the thyroid gland, also known as Hashimoto's thyroiditis. In autoimmune conditions the body's immune system seems to turn against some of its own tissues.

complications arising from previous surgery to the thyroid gland or from radioactive iodine treatment, both of which are used to treat overactivity of the thyroid gland.

an inherited incomplete development of the thyroid gland.

as a consequence of treatment with certain medicines such as propylthiouracil, carbimazole, amiodarone and lithium.

taking large amounts of iodine for example in some cough syrups or excessive amounts of dietary supplements made from or containing kelp.

What are the symptoms?

Decreased metabolism can affect every organ of the body including brain, heart, skin, intestine and muscles.

Symptoms tend to appear gradually over a long period of time. For this reason, decreased metabolism in the elderly is often mistaken for changes that take place naturally with age.

Typical symptoms of decreased metabolism are:

decreased tolerance of cold environments

depression and lethargy

weight gain

constipation

dry, rough skin

coarsening of the facial features and a deep voice

thin, dry hair

poor memory - among the elderly this may be the only symptom of decreased metabolism

in severe cases, dementia.

How can hypothyroidism be prevented?

People who have been treated at some time in their lives for an overactive thyroid gland have an increased risk of developing underactivity, because the methods of treatment reduce the amount of functioning thyroid tissue. Thus, it is advisable to have the thyroid gland checked once a year.

Avoid taking natural medicine and dietary supplements that contain large amounts of iodine.

How does the doctor make a diagnosis?

When hypothyroidism is suspected the diagnosis can be confirmed by taking a blood sample to measure the concentration of thyroid stimulating hormone (TSH). This hormone is produced in the pituitary gland of the brain and also plays an important part in regulating metabolism.

When the amount of T4 and T3 in the blood is too low, the pituitary gland sends a signal to the thyroid gland to work harder by releasing more TSH. This increase in TSH shows that the thyroid gland is underactive and needs to be stimulated.

Occasionally, the doctor may order further blood tests in order to detect an abnormality of the immune system, which may help the diagnosis.

Sometimes, especially if the patient has a goitre (enlargement of the thyroid), the doctor might also recommend an ultrasound examination.

How is a hypothyroidism treated?

Permanently decreased metabolism requires lifelong treatment with thyroxine tablets.

Usually, a small dose is recommended to start with, which is then increased gradually until an accurate dose has been reached.

When this has been achieved, it is usually necessary to check the patient's metabolic rate only once a year.

The hormone tablets have virtually no side effects. However, patients should watch out for symptoms of increased metabolism, which may occur if the dose is too high.

In the UK, patients taking thyroxine treatment for hypothyroidism are entitled to free prescriptions.

Future prospects

With proper treatment, people with a decreased metabolic rate are able to lead completely normal lives.

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