The Thyroid Gland
Some of the more common hormonal disorders are associated with the thyroid gland, which is part of the endocrine system. This system is a collection of glands that secrete chemicals called hormones directly into the bloodstream. Together with the nervous system and the immune system, the endocrine system helps the body to cope with different events and stresses.
The thyroid gland is situated at the front of the throat, below the larynx (Adam’s apple), and comprises two lobes that lie on either side of the windpipe. The thyroid gland secretes hormones to regulate many metabolic processes, including growth and energy expenditure. If the thyroid gland is overactive or sluggish, the metabolism will be affected, leading to a variety of symptoms that are easily misdiagnosed. Around one in 20 people will experience some form of thyroid dysfunction in their lifetime. Women are more susceptible than men.
An overactive thyroid is known as hyperthyroidism, and this condition tends to affect women more than men. Around two in every 100 women will experience some degree of hyperthyroidism. The most common cause is Graves’ disease, which is due to an immune system abnormality. Other causes of an overactive thyroid include local inflammation (thyroiditis), nodules or lumps. There is no cure for hyperthyroidism, but it can be successfully managed with treatments such as anti-thyroid medication.
The symptoms of hyperthyroidism include:
- Accelerated heart rate or palpitations
- Muscle weakness and trembling
- Unexplained weight loss
- Sensitivity to heat
- Sleeping difficulties
- Nervousness, agitation and anxiety
- Changes in menstruation, including scantier flow and increased cycle length.
The most common cause of hyperthyroidism is Graves’ disease. An abnormality of the immune system is the cause. The immune system is a collection of special cells and chemicals that fight infection from foreign agents, such as bacteria and viruses. A key element of the immune system is the antibody, which is a type of tailor-made ‘poison’ produced by lymphocytes (white blood cells) to kill a particular foreign agent. In a person with Graves’ disease, the immune system manufactures antibodies which behave like TSH and stimulate the thyroid uncontrollably. Less than one per cent of the population has Graves’ disease. Eight times more women than men have this condition. Graves’ disease is more common in middle age, although children and adolescents can also be affected.
Hypothyroidism is the most common thyroid disorder, and it is thought to affect around six to 10 per cent of women. The prevalence rises with age – up to a quarter of women over the age of 65 years may be affected. Men are also affected, but less frequently. Hypothyroidism can be either primary or secondary. Primary hypothyroidism means that the thyroid gland itself is diseased, while secondary hypothyroidism is caused by problems with the pituitary gland, the brain structure that supervises the thyroid gland. The most common cause of primary hypothyroidism is the autoimmune condition Hashimoto’s disease.
Symptoms of hypothyroidism
The symptoms of hypothyroidism can be mild, moderate or severe. In its severest form (myxoedema coma), hypothyroidism is potentially fatal and requires urgent medical treatment. Symptoms of hypothyroidism can include:
- fatigue and low energy levels
- slow heart rate
- unexplained weight gain
- intolerance to cold temperatures
- fatigued and aching muscles
- dry, coarse skin
- puffy face
- hair loss
- problems with concentration
- goitre (enlarged thyroid gland).
Causes of hypothyroidism
The causes of hypothyroidism include:
- Iodine deficiency disorder – lack of sufficient iodine in the diet can prevent the thyroid gland from making hormones. The thyroid enlarges as it attempts to comply with the pituitary gland’s ceaseless chemical messages to produce more hormones. An enlarged thyroid is known as a goitre. Babies and children can be stunted and severely brain damaged by iodine deficiency because thyroid hormones are needed for normal growth and development.
- Hashimoto’s disease – an autoimmune disorder. White blood cells and antibodies of the immune system attack and destroy the cells of the thyroid gland. Without treatment, death can occur within 10 to 15 years.
- Treatment for hyperthyroidism – treatments for hyperthyroidism (including drugs, surgery and radioactive iodine) frequently lead to hypothyroidism.
- Surgery – the primary treatment for thyroid cancer, and also a treatment for hyperthyroidism, surgery will lead to hypothyroidism if the thyroid gland is removed or if insufficient is left in place.
- X-rays – radiation treatments (in the past used for acne, tonsillitis and adenoid problems) can lead to hypothyroidism in later life. These treatments are not used today.
- Particular drugs – including lithium and the heart drug amiodarone can interfere with the normal processing of iodine and the production of thyroid hormone.
- Birth defects – sometimes, a baby is born with a congenital defect of the thyroid gland (which affects hormone production) or the thyroid may be completely absent. Without treatment, this can lead to brain damage and stunted growth.
- Pituitary gland dysfunction – the pituitary gland doesn’t make enough thyroid stimulating hormone to prompt the thyroid to produce T3 and T4.
- Hypothalamic dysfunction – the functioning of the pituitary is influenced by another brain structure called the hypothalamus, through the thyrotropin-releasing hormone. Problems with the hypothalamus can affect the pituitary and, in turn, the thyroid gland.