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This fact sheet provides comprehensive information on thyroid dysfunction, including definitions, prevalence, causes, signs and symptoms, pathophysiology, diagnosis, management, patient support, and further resources for both hyperthyroidism and hypothyroidism. It also includes references and external links.
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Definition British Medical Journal (BMJ) Best Practice describes thyroid function in the following way: ‘The thyroid gland produces, stores, and secretes thyroxine (T4) and triiodothyronine (T3) through a negative feedback process involving the hypothalamus and pituitary gland. Thyroid dysfunction can result when any part of this process is affected, and is usually characterised by the presence of high or low levels of thyroid- stimulating hormone (TSH, secreted by the pituitary gland) and free thyroid hormones.’^1
Hyperthyroidism occurs when there is an excess of circulating thyroid hormones (T3 and T4) due to an overactive thyroid gland. This is referred to as thyrotoxicosis.
Hypothyroidism is the result of impaired production of the thyroid hormones.
For further information about the definitions of each of these conditions, and about the overt and subclinical presentations of each, access the National Institute for Health and Care Excellence (NICE) clinical knowledge summaries (CKS) Hyperthyroidism – Definition and Hypothyroidism – Definition.
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Prevalence and incidence Hyperthyroidism It has been reported that in Europe, the total prevalence (diagnosed and undiagnosed) of hyperthyroidism is 0.75 percent. A consensus guideline states the prevalence of hyperthyroidism in women is 0.5 to 2 percent, and it is ten times more common in women than in men.
In England, the prevalence of subclinical hyperthyroidism was found to be 2.1 percent in a cross-sectional screening survey of 5950 adults aged over 65 years. 4
Hypothyroidism Primary hypothyroidism is also ten times more common in women than in men. It has been reported that in Europe, the total prevalence (diagnosed and undiagnosed) of hypothyroidism is three percent, with an incidence rate of 370 per 100,000 per year in women and 72.5 per 100,000 per year in men.
Secondary hypothyroidism is rare, with an estimated incidence of between 1 per 20,000 and 1 per 80, people in the general population.
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Causes/risk factors Hyperthyroidism There are several causes of primary hyperthyroidism ; the most common are Graves’ disease, thyroid nodules, and medicines such as amiodarone and lithium (after long-term use).
Causes of secondary hyperthyroidism include high levels of a hormone called human chorionic gonadotrophin, which can stimulate the thyroid gland and suppress TSH; tumours on the pituitary gland; and a rare condition called thyroid hormone resistance syndrome, where the pituitary gland is resistant to thyroid hormones. 5
Risk factors include:
For further information, access the NICE CKS Hyperthyroidism – Causes and Hyperthyroidism – Risk factors.
Hypothyroidism Causes of primary hypothyroidism include:
It should be noted that about 15 percent of people treated with anti-thyroid medicines for Graves’ disease (such as carbimazole and propylthiouracil) will develop hypothyroidism 10 to 20 years later. 7
Causes of secondary hypothyroidism relate to pituitary and hypothalamic dysfunction. 7
For more information, access the NICE CKS Hypothyroidism – Causes****.
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Pathophysiology (mechanism of disease)
Thyroid hormones are essential for normal growth, development and cellular metabolism. Circulating thyroid hormone levels are normally controlled through the process of negative feedback on the hypothalamus and pituitary gland. 2
The following video gives an overview of how thyroid hormones are produced and function in a person who does not have thyroid dysfunction.
Human Physiology – Thyroid hormone feedback and function
When this process becomes disrupted due to one of the previously discussed causes of thyroid dysfunction, thyroid dysfunction occurs. In this case, the production and serum concentration of TSH, T and T4 may be deranged.
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Prognosis and complications The prognosis for both conditions is variable depending on whether the conditions are overt or subclinical.
Access the NICE CKS Hyperthyroidism – Prognosis and Hypothyroidism – Prognosis , which cover the prognosis for each condition in detail.
In addition to individual complications for each condition, both hyper and hypothyroidism are linked to an increased risk of heart failure and cardiac complications. Hyperthyroidism increases the risk of atrial fibrillation , and hypothyroidism is linked to coronary heart disease and stroke. 8,
Access the NICE CKS Hyperthyroidism – Complications and Hypothyroidism – Complications , which cover complications for each condition in detail.
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Diagnosis/detection
The following Pharmaceutical Journal article offers more detail on the changes in the production of thyroid hormones in hyper and hypothyroidism, and the causes of this: Thyroid disorders: causes, diagnosis and treatment.
Another Pharmaceutical Journal article covers Thyrotoxicosis and hyperthyroidism: causes, diagnosis and management.
The British National Formulary offers two treatment summaries for antithyroid drugs and thyroid hormones , which link to the individual monographs for each therapy.
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Patient support The British Thyroid Foundation is a charity dedicated to supporting people with thyroid disorders, and helping their families and people around them to understand the condition. They also offer a series of quick guides which offer information about thyroid disorders and related issues.
Thyroid UK is a charity that offers quality information and support to people with both diagnosed and undiagnosed thyroid disorders.
The NHS website has Overactive thyroid (hyperthyroidism) and Underactive thyroid (hypothyroidism) pages.
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Further resources The British Thyroid Association is the only national professional organisation in the UK composed of research doctors and consultants who are accredited for having completed higher professional training in thyroid and other endocrine diseases. They offer a page dedicated to Professional resources. They also offer Current BTA guidelines and statements , with links to BTA guidelines and guidelines from other bodies.
The British Thyroid Foundation’s article Older patients and thyroid disease explores the diagnosis and treatment of thyroid disorders in older people.
The NICE page Thyroid disorders links to all NICE products on thyroid disorders and includes any guidance and advice.
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External websites CPPE is not responsible for the content of any non-CPPE websites mentioned on this page or for the accuracy of any information to be found there.
All web links were accessed on 14 January 2022.
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References
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Last review: January 2022 Next review due: January 2023
