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. It is often detected incidentally, although some people may have symptoms of hypothyroidism or hyperthyroidism. The 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. They indicate increased cardiovascular morbidity and mortality, an increased risk of osteoporosis and potential links to dementia.
This guideline covers investigating all suspected thyroid dysfunction and managing primary thyroid disease (related to the thyroid rather than the pituitary gland). There is variation in how thyroid disease is investigated and managed in primary and secondary care. There are currently no standardised diagnostic or referral criteria in the UK to guide decision making in primary care for people with structural thyroid abnormalities or enlargement. In secondary care, there is significant variation in the types of diagnostic tests and imaging used, as well as in surgical and non-surgical management and follow-up protocols. Standardisation in thyroid hormone replacement strategies for people with hypothyroidism is currently lacking. In addition, guidance on optimal treatment and follow-up strategies is needed for managing thyrotoxicosis, which is usually done by shared care between primary and secondary care. Opinions regarding the need to treat subclinical thyroid dysfunction, especially in older people, vary widely.
This guideline also aims to improve the diagnosis, management and follow-up of non-malignant thyroid enlargement associated with normal thyroid function.