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Disorders of the thyroid axis

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Thyroid disease includes thyroid enlargement and thyroid hormone dysfunction

  • thyroid enlargement may be benign, resulting in nodules or goitre, or malignant in people with thyroid cancer
  • conditions causing thyroid dysfunction can be broadly divided into those that result in thyroid gland underactivity (hypothyroidism) or overactivity (thyrotoxicosis)
  • thyroid enlargement is common
    • about 15% of the UK population have clinically detectable goitres or thyroid nodules, and the lifetime risk of developing a thyroid nodule is around 5 to 10%
    • in many cases, thyroid glands harbouring malignancy are clinically indistinguishable from those that are not. Most people with a non-malignant enlarged thyroid gland and normal thyroid function need no treatment.

Hypothyroidism is a condition of thyroid hormone deficiency and is usually caused by autoimmune Hashimoto's thyroiditis

  • primary hypothyroidism refers to conditions arising from the thyroid gland rather than the pituitary gland (secondary hypothyroidism)
  • hypothyroidism is found in about 2% of the UK population and in more than 5% of those over 60
  • women are 5 to 10 times more likely to be affected than men
  • long-term consequences of hypothyroidism include cardiovascular disease and an increase in cardiovascular risk factors, including hypercholesterolaemia.

Thyrotoxicosis is a disorder of excess circulating thyroid hormones caused by increased production and secretion (hyperthyroidism) or the release of (thyroiditis) stored thyroid hormones

  • in the UK, autoimmune hyperthyroidism (Graves' disease) is the most common form, accounting for 60 to 80% of cases
  • thyrotoxicosis is a common endocrine disorder with a prevalence of around 2% in UK women and 0.2% in men
  • Graves' disease is caused by a genetic predisposition to developing stimulating thyroid autoantibodies and occurs mostly in women aged 30 to 60 years
  • thyrotoxicosis affects 1 to 2 children per 10,000
  • children may be severely affected, with poor educational performance often being an early feature
  • long-term consequences of hyperthyroidism include increased cardiovascular morbidity and mortality and bone-related complications, including osteoporosis.

Subclinical thyroid dysfunction is a biochemical diagnosis where serum thyroid-stimulating hormone (TSH) levels are outside the reference range, and circulating thyroid hormone levels (thyroxine [T4] and tri-iodothyronine [T3]) are within the reference range

  • often detected incidentally, although some people may have symptoms of hypothyroidism or hyperthyroidism
  • prevalence of subclinical thyrotoxicosis is 0.5 to 10% and that of subclinical hypothyroidism is 4 to 20%; these wide ranges reflect differences in the studied populations
  • data on the long-term consequences of subclinical thyroid dysfunction largely come from people over 65
    • indicate increased cardiovascular morbidity and mortality, an increased risk of osteoporosis and potential links to dementia.


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