thyroid gland disorders

Thyroid disorders explained

Hypothyroidism; Hyperthyroidism; Thyroid nodules and swellings; Diagnosing thyroid disorders; Prevention; Thyroid disorders and pregnancy

Women are more likely than men to suffer from thyroid problems, which can cause depression and tiredness

The thyroid is a butterfly-shaped gland you can feel at the base of your neck, just below your Adam's apple. Two lobes - the butterfly 'wings' - fit to either side of your windpipe. This gland is one of the most important in your body as one of the hormones it produces regulates the body's metabolism.

The thyroid gland is a manufacturing and storage facility for thyroid hormone, which is often referred to as the body's metabolic hormone. Among other actions, thyroid hormone stimulates enzymes that combine oxygen and glucose, a process that increases the basal metabolic rate and body heat production. Thyroid hormone also helps maintain blood pressure, regulates tissue growth and development, is critical for skeletal and nervous system development and plays an important role in the maturing of the reproductive system.

Women are five to ten times more likely than men to have thyroid dysfunction and some types of thyroid disease run in families. Although many women get thyroid disorders, doctors often fail to recognise it because the wide variety of symptoms are similiar to other illnesses.

Disorders of the thyroid

Hypothyroidism, where the thyroid releases too little hormone so the body's metabolism goes too slowly.

Hyperthyroidism, where the thyroid releases too much hormone and the body's metabolism goes too fast.

Thyroid nodules and swellings. The tissue of the thyroid can overgrow, resulting in a nodule, or small lump, in part of the gland. Some of the lumps can be active while others are inactive. A small percentage of the inactive lumps may be cancerous.

Hypothyroidism
Hypothyroidism means that the thyroid gland is producing too little hormone. It's a common condition, occurring usually in the second half of life with 90 per cent of the sufferers being female. Hypothyroidism often goes undiagnosed for years because its signs and symptoms can easily be mistaken for other conditions.

The leading cause of hypothyroidism is called Hashimoto's thyroiditis. Named after the Japanese doctor who first described it in detail, Hashimoto's thyroiditis is an autoimmune disease. This means that the immune system is working against the thyroid - so it's actually producing antibodies to the gland as if it were a foreign substance that needed to be destroyed. The damage caused by the antibodies results in decreased production of thyroid hormone.

Hypothyroidism may also result from medical treatment of an overactive thyroid gland, which may be with radioactive substances or by surgery. It can also occur during or after pregnancy.

Symptoms of hypothyroidism
When too little thyroid hormone is released, the body's metabolic rate decreases and the body slows down. There are numerous symptoms associated with this condition, including:

Coarse, dry hair/hair loss

Slow heart rate

Constipation

Poor memory

Trouble concentrating

Hoarseness/husky voice

Irregular/heavy menstruation

Muscle aches

Infertility

High cholesterol

Goitre (enlarged thyroid gland)

Treating hypothyroidism
Hypothyroidism, including Hashimoto's thyroiditis, is the simplest of the three types of thyroid disorders to treat. It requires a daily dose of a substitute thyroid hormone called L-thyroxine. You and your doctor will work together to find the right dose for you; this determination will be made over subsequent visits and will depend on a number of blood tests and how you are feeling.

Hypothyroidism patients take the drug for the rest of their lives, probably needing several changes in the dose over time. Blood tests will be taken periodically to determine if the dose should be raised or lowered to maintain the right levels of thyroid hormone and thyroid-stimulating hormone (TSH).

Side effects: if your dose is too low and you remain somewhat hypothyroid, you could be at risk for arteriosclerosis (hardening of the arteries) due to elevated cholesterol levels. If your dose is too high and you become somewhat hyperthyroid, you may notice symptoms of that disorder. Over time, thyroid hormone excess could put you at higher risk for heart attack or osteoporosis.

Hyperthyroidism
Hyperthyroidism means that the thyroid gland is producing and releasing too much hormone. It is most common within the 30-60 age group, and around 90 per cent of cases occur in women.

The leading cause of hyperthyroidism is called Graves' disease. As with Hashimoto's thyroiditis, it is an autoimmune disorder characterised by antibodies that attack the thyroid. The two diseases differ, however, because in the case of Graves' disease, the antibodies cause excess growth to cause general enlargement of the thyroid gland, which then overproduces thyroid hormone. The antibodies may also attack eye muscle tissue and the skin on the front of the lower leg. Graves' disease was named for Robert Graves, an Irish physician who first discussed this form of hyperthyroidism, but it also goes by the name 'diffuse toxic goitre'.

Hyperthyroidism can also be caused by nodules that are overproducing thyroid hormone, a condition known as 'toxic multinodular goitre'. It can also develop during or after pregnancy, or after hypothyroid treatment with an excess of thyroxine.

Symptoms of hyperthyroidism
When too much thyroid hormone is released, the body's metabolic rate increases and the body speeds up. Signs and symptoms of hyperthyroidism include:

Nervousness/irritability

Weight loss

Fast/irregular heart rate

Heat intolerance/increased perspiration

Changes in appetite

Sleep disturbances (such as insomnia)

Muscle weakness

Trembling hands

More frequent bowel movements

Decreased menstrual flow

Exophthalmos (eyes that seem to be popping out of their sockets)

Goitre (enlarged thyroid gland)

Treating hyperthyroidism
If you are diagnosed with hyperthyroidism, including Graves' disease, your doctor will consider several factors to determine the best treatment for you. These factors include your age, your general health and the severity of the disorder.

Medication. The first type of treatment that your doctor will use is likely to be medication with an antithyroid drug. Antithyroid drugs are designed to interfere with the thyroid gland's uptake of iodine. Because iodine is essential for thyroid hormone production, this treatment results in lowered levels of thyroid hormone. The commonest drug used in the UK for this condition is Carbimazole. Drugs may also be given to help with the symptoms of hyperthyroidism; for instance Propanolol helps to control palpitations and tremor.

Surgery. Removal of part of the thyroid gland (partial thyroidectomy) is considered when there is a large goitre, when drug therapy is unsuitable or when there is recurrence after medication. If a nodule is causing your hyperthyroidism, surgical removal of the nodule may well be your best option. If the entire gland is overactive, it will be removed and you will need to take synthetic thyroid hormone for the rest of your life.

Radioactive iodine therapy. This treatment is sometimes used, especially if the patient is over 40, the condition is difficult to control with drugs or there is recurrence after thyroidectomy. Over several weeks after the dose is given, the gland shrinks and therefore the blood levels of thyroid hormone drop. Patients report feeling better within three to six weeks and most are completely cured of hyperthyroidism within six months (for most it is three to four months). There are no side effects associated with radioactive iodine, except an occasional sore throat.

An important issue to consider regarding hyperthyroidism therapy is that many patients will become hypothyroid. Be aware of the symptoms of that disorder so you can get the proper treatment.

When people with Graves' disease get better after thyroid treatment, they should consider their status as unstable. Remission may be permanent, but the thyroid should be checked once a year to be sure. Severe stress can aggravate a recurrence.

Thyroid nodules and swellings
Swellings of the thyroid gland are common, affecting up to ten per cent of people, especially women. In some cases the swelling involves the whole gland, which is then known as a 'goitre', while in many there are individual swellings known as 'nodules'. These may range from as small as a millimetre to as large as several centimetres and may be clumps of thyroid cells or fluid filled cysts. The cause of these swellings is often not known, although in some parts of the world is linked to a deficiency of iodine.

Most nodules are not associated with symptoms, are never detected and are harmless (90 per cent are benign). Nodules can, however, indicate an underlying problem with the thyroid and there is always a slight chance that a thyroid nodule is cancerous, so it is important to have all growths assessed by your doctor. There are three main ways in which a thyroid nodule can cause problems:

A nodule may be making too much thyroid hormone.

A few thyroid nodules may be due to cancer.

Very occasionally nodules or swellings can be large enough to press against the windpipe and cause difficulty with swallowing or a cough.

Treating nodules
A biopsy of the nodule will show if it is benign, as most are, or malignant. If benign, it requires monitoring rather than treatment. If a biopsy is indeterminate, or it identifies a malignancy, surgery is the appropriate treatment. Most thyroid cancers are curable.

Thyroidectomy is done under general anaesthesia and takes about two hours. How much of the thyroid gland is removed depends upon what the surgeon finds when he begins the operation. During the operation the surgeon may send some thyroid tissue to the laboratory for a very quick examination (a procedure known as a 'frozen section'). If cancerous cells are present, the surgeon will proceed to remove more of the thyroid. If the cancer has spread outside the thyroid, the lymph nodes in the neck may also be removed.

Some patients will need to take radioactive iodine six weeks after their surgery. This treatment will destroy any residual cancerous tissue. All patients also will begin lifelong thyroid hormone replacement therapy.

Side effects: As with other surgery, the minor risks include infection, bleeding and scar tissue on the neck. Major side effects from surgery are rare and involve complications to neck structures close to the thyroid. For example, 1 percent of patients develop speech problems due to nerve damage. If the parathyroid glands are damaged during surgery, patients will require calcium supplements and possibly other drugs.

Diagnosing thyroid disorders
To make the diagnosis in cases of thyroid disorder, your doctor will first ask about symptoms and then examine you, paying particular attention to your neck. He or she will probably perform one or more investigations, some of which will involve a referral to a hospital specialist.

Blood tests
In cases of hypo- and hyperthyroidism there is an abnormal level of thyroid hormone circulating in the blood. Diagnosis of these conditions largely depends on a series of blood tests to measure levels of:

Thyroid hormone. The thyroid gland actually consists of two hormones: thyroxine, known as T4, and triiodothyronine, known as T3. Both these hormones will probably be measured.

Thyroid-stimulating hormone (TSH). To get an even clearer picture, the laboratory will probably also test blood for TSH levels. TSH is produced by the pituitary gland in the brain as a signal for the thyroid to produce more or less thyroid hormone. The pituitary gland is like a sensor on a thermostat; if it senses that there is not enough thyroid hormone in your blood, it releases TSH to tell your thyroid to produce more. Likewise, if your pituitary senses there is too much thyroid hormone in the blood already, it will decrease its production of TSH.

Antibodies to thyroid tissue. These may be raised if there is autoimmune disease such as Hashimoto's thyroiditis.

If hypothyroidism is suspected based on the presence of several symptoms, a diagnosis can be confirmed if your thyroid hormone (T3 and T4) levels are low to normal and your TSH is high. Antithyroid antibodies may suggest Hashimoto's thyroiditis as the cause.

If hyperthyroidism is suspected based on the presence of several symptoms, a diagnosis can be confirmed if your thyroid hormone (T3 and T4) levels are high and your TSH is low. To determine if Graves' disease is the cause, your doctor can check your blood for thyroid stimulating antibodies or give you a radioactive iodine uptake test.

Radioactive iodine uptake test
Iodine is essential for the production of thyroid hormone, so the thyroid absorbs it from the blood. During a radioactive iodine uptake test, you will swallow a small amount of iodine that has been made slightly radioactive. The thyroid will absorb and metabolise 20 per cent of this iodine within 24 hours. Special equipment is then used to measure the amount of radioactivity over the thyroid gland. If you have Graves' disease, the amount of iodine in the thyroid will be elevated. If you have other forms of hyperthyroidism, such as taking too much thyroid medication or Hashimoto's disease, it will be suppressed.

Diagnosing thyroid nodules
If you have a nodule or swelling in your thyroid you should have the nodule evaluated by a hospital specialist. In addition to ordering thyroid blood tests the doctor will want to examine the structure of your thyroid gland. There are three tests that can provide a structural view of your thyroid:

Biopsy. The most accurate test is a biopsy called a fine needle aspirate. A very thin needle is inserted into the gland and at least six samples of tissue are sucked out (aspirated). These samples are then analysed under a microscope, and most of the time (more than 90 per cent) they are non-cancerous.

Thyroid scan. As with a radioactive iodine uptake test (described above), for a thyroid scan you would swallow a radioactive chemical (usually iodine or technetium). A special camera is then used to show the size, shape and function of the gland based on how much of the radioactive material was absorbed. This can determine whether the lumps are 'hot' (usually benign, just overactive) or 'cold' (inactive and either benign or malignant).

Ultrasound. An ultrasound test uses sound waves to determine whether a nodule is filled with fluid or if it is solid. This test also can find other nodules that can't be felt with a manual examination.