Thyroid Diseases

Thyroid Diseases

What is the thyroid gland?

The thyroid gland is located in the throat and is responsible for producing thyroid hormones. These hormones act on cells throughout the body to help control metabolism and ensure all the body systems are functioning properly.

Sometimes, the normal functioning of the thyroid gland can become disrupted, resulting in an over- or under-production of thyroid hormone, which can have widespread consequences throughout the body.

What is overactive thyroid (hyperthyroidism)?

An overactive thyroid (also called hyperthyroidism or thyrotoxicosis) is when the thyroid gland produces more thyroid hormones than normal. The thyroid gland may become enlarged, or contain nodules (lumps) of overactive tissue.

This excess thyroid has the effect of speeding up metabolism throughout the body. Symptoms may include:

  • Person is jumpy and agitated
  • Pulse is fast and irregular
  • Weight loss – despite normal food intake
  • Excessive sweating and warm, clammy hands
  • Intolerance to heat
  • Tremors/shaking
  • Vomiting and diarrhoea.

Overactive thyroid occurs in women more often than men.

What causes overactive thyroid?

The most common cause of overactive thyroid is a condition called Grave’s disease. This is thought to be an autoimmune disease (meaning that the person’s immune system starts to attack their own body tissues) in which the thyroid gland loses its ability to respond to normal control, resulting in a general overactivity of the thyroid gland. Graves’ disease is genetic and tends to run in families – however, stress, smoking, and certain medications and viruses may set it off.

Other causes of overactive thyroid include the development of thyroid nodules, inflammation of the thyroid following a virus or during pregnancy, and excessive iodine intake. Key sources of iodine in the diet are seafood, milk, bread and salt.

How is overactive thyroid treated?

Your doctor will diagnose overactive thyroid by asking you about your symptoms and conducting a blood test to look at levels of thyroid hormones in your blood.

There are a number of treatment options for overactive thyroid. If your hyperthyroidism is mild and you are young, you may be given antithyroid medications, which act to reduce production of thyroid hormones. Your doctor may also give you other drugs, called beta-blockers, to control your symptoms until your thyroid levels are under control. Another treatment option is radioactive iodine – this is a liquid that is swallowed and taken up by the thyroid gland, destroying most or all of the thyroid tissue. This treatment is generally only used in older patients.

If your thyroid gland has become significantly enlarged, your doctor may also recommend surgery to remove all or part of the thyroid gland, in order to permanently cure the hyperthyroidism. However, there is a risk when taking radioactive iodine or undergoing surgery that the amount of thyroid production can be reduced too much – i.e., leading to under-active thyroid (hypothyroidism).

What is under-active thyroid (hypothyroidism)?

An under-active thyroid (also called hypothyroidism or, when it develops in adults, myxoedema), is when the thyroid gland does not produce enough hormones to keep the body functioning efficiently.

Under-active thyroid is more common in women than men, and its incidence increases with age. However, it can also be present from birth or develop during childhood. Symptoms are often quite subtle and may only become more obvious as the condition progresses. They may include:

  • Person may feel lethargic and easily fatigued (tired out)
  • Muscle aches and cramps
  • Intolerance to cold
  • Dry, flaky skin
  • Coarse, brittle hair and thinned eyebrows
  • Hoarse voice
  • Weight gain
  • Slow heart rate
  • Constipation.

What causes under-active thyroid?

The most common cause of hypothyroidism is a condition called Hashimoto’s thyroiditis – an autoimmune disease in which the body’s immune system starts to attack the thyroid tissue, causing inflammation and severe damage to the thyroid gland. This condition is partly hereditary.

Another common cause of under-active thyroid disease is over-treatment for hyperthyroidism, through medication, radioactive iodine or surgery (with medication, it is reversible). Severe lack of iodine in the diet can also cause hypothyroidism – although this is a rare cause in this country, due to addition of iodine in salt.

How is under-active thyroid treated?

Your doctor will diagnose under-active thyroid by asking you about your symptoms and conducting a blood test to look at your levels of thyroid hormones.

Under-active thyroid can be treated with the hormone, thyroxine.

Reviewed: November 9, 2006


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