A goitre is an enlargement of the thyroid gland. This gland is situated at the front of the throat, below the Adam's apple (larynx). It comprises two lobes that lie on either side of the windpipe and are joined in front by an isthmus. The thyroid gland secretes hormones to regulate many metabolic processes, including growth and energy expenditure. The thyroid gland is
controlled by the pituitary gland, which is located in the brain. The pituitary prompts the thyroid to make its hormones - including thyroxine (T4) and tri-iodothyronine (T3) - by releasing thyroid-stimulating hormone (TSH). However, the thyroid can't manufacture its hormones without sufficient dietary iodine.
If a person's diet is low in iodine, the pituitary keeps sending chemical messages to the thyroid, but in vain. The thyroid gland enlarges as it attempts to comply with the pituitary's demands. Apart from iodine deficiency, other causes of goitre involve conditions of the thyroid - such as nodules, cancer, hyperthyroidism and hypothyroidism.
In many cases there are no symptoms apart from the appearance of a swelling in the neck. The size of a goitre can range from very small and barely noticeable to very large. Most goitres are painless. An inflamed thyroid (thyroiditis) can be painful. If your thyroid makes too much or too little thyroxine, this can cause a range of symptoms. See separate leaflets. A large goitre may press on the trachea (windpipe) or even the oesophagus (gullet) behind the trachea. This may cause difficulty with breathing or swallowing.
A dietary deficiency of iodine, which is a key ingredient in the manufacture of thyroid hormone, can cause goitre in certain populations. Such a goitre is termed endemic, meaning a high incidence of goitre (in more than 10 percent of the population) occurs in a specific community or geographic area. Inadequate dietary intake of iodine, and thus endemic goitre, typically occurs more commonly in fresh water and lake areas than on the sea coast, because of the lack of iodine in fresh water.
Ingesting large quantities of goitrogenic foods or drugs, which contain substances that decrease thyroid hormone production. Goitrogenic drugs include lithium, cobalt, phenylbutazone (in some anti-inflammatory medications) and iodides (excessive iodine intake can also cause goitre). This cause of goitre is usually termed sporadic i.e. goitre arises in nonendemic areas as a result of a stimulus that does not affect the population generally. However, sometimes dietary or waterborne goitrogens may act together with iodine deficiency to produce goitre in a population.
Treatment depends on the cause, the size of the goitre, and whether it is causing symptoms. Goitre caused by iodine deficiency can be helped with the introduction of iodine-rich foods into the diet, such as seafood and iodised salt. Hyperthyroidism is managed with drugs that slow the activity of the thyroid. If these fail to work, part or all of the thyroid gland is surgically removed. Alternatively, some or all of the thyroid's hormone-producing cells can be destroyed with radioactive iodine treatment. Hypothyroidism is treated by lifelong hormone replacement therapy. Benign thyroid nodules are shrunk with medications, destroyed with radioactive iodine treatment or surgically removed, depending on the type. Cancer of the thyroid is treated by surgical removal of the gland, followed by radioactive iodine treatment.