What are disorders of the thyroid gland?
Goitre (Enlargement of the thyroid)
Goitre is the general term for enlargement of the thyroid gland. The swelling can be diffuse, where the whole gland is generally enlarged or nodular where irregular local areas of the gland become swollen. Enlargement of the thyroid gland can occur with no associated abnormal function (euthyroid or non-toxic goitre) but also in conditions where under-activity (hypothyroidism) or over-activity of the gland (hyperthyroidism) is evident.
Myxoedema (Hypothyroidism - under active thyroid)
This is the condition caused by under-activity of the thyroid gland with impaired production of thyroid hormone. This is usually caused by deficiency of dietary intake iodine, impairment of pituitary function or inflammation or primary disease of the thyroid gland.
When iodine becomes severely deficient the thyroid gland fails to produce sufficient thyroid hormone. The pituitary gland responds by producing increasing amounts of TSH (thyroid-stimulating hormone) in an attempt to force an increase in production of thyroid hormone.
When production of TSH is impaired by disease of the pituitary gland there is insufficient stimulation of the thyroid with consequent reduction in output of thyroid hormone.
Hashimoto's thyroiditis is an inflammatory disease of the thyroid glandular tissue and impairs the ability to produce thyroid hormones. The gland becomes enlarged as a result of the inflammation.
The effects of ionising radiation, either from therapeutic use or accidental exposure, and surgical removal of the thyroid gland may produce the syndrome of hypothyroidism.
Thyrotoxicosis (Hyperthyroidism - overactive thyroid)
This is the condition that results from increased action of thyroid hormone. Around 70% of cases are caused by a condition called Graves' disease. This results from an autoimmune disease in which the body’s immune system produces antibodies, which act like TSH and uncontrollably stimulate the thyroid gland. The gland responds by producing an excessive amount of hormone and goitre can result from the massive over-activity of glandular tissue.
Toxic multinodular goitre accounts for around 20% of cases and usually develops from chronic (euthyroid) nodular goitre following treatment with iodine.
The remaining 10% of cases fall due to causes such as toxic adenoma (a toxic non-malignant tumour), thyroid cancer or its metastases (malignant thyroid disease TSH-secreting pituitary tumour or thyroiditis (inflammation of the thyroid gland)
