thyrotoxicosis

Last edited 12/2019 and last reviewed 10/2023

Hyperthyroidism is a disease where there is excess production and release of thyroid hormone from the thyroid gland resulting in inappropriately high serum levels (1)

• although the term thyrotoxicosis has been used synonymously with hyperthyroidism, some experts have tried to differentiate the two terms
• hyperthyroidism - excess synthesis and secretion of thyroid hormones from the thyroid gland
• thyrotoxicosis  - excessive amounts of circulating thyroid hormones, but includes extrathyroidal sources of thyroid hormone or by a release of preformed thyroid hormones into the circulation (1,2)

Hyperthyroidism is characterised by normal or high thyroid radioactive iodine uptake – known as thyrotoxicosis with hyperthyroidism or true hyperthyroidism.

• thyrotoxicosis without hyperthyroidism  - due to extrathyroidal sources of thyroid hormone or by a release of preformed thyroid hormones into the circulation with a low thyroid radioactive iodine uptake e.g. – thyroiditis is a frequent cause  (1)

Hyperthyroidism can be:

• overt - characterised by low serum thyroid-stimulating hormone (TSH) concentrations and raised serum concentrations of thyroid hormones: thyroxine (T4), tri-iodothyronine (T3), or both.
• subclinical - characterised by low serum TSH, but normal serum T4 and T3 concentrations (1).

Prevalence of hyperthyroidism is 0·8% in Europe, and 1·3% in the USA

• the condition increases with age
• more common in women
• Graves disease is the most common cause
• thyroid storm usually develops in 1%-2% of thyrotoxicosis patients (2,3)

Tests for people with confifirmed thyrotoxicosis (4):
Adults

• differentiate between thyrotoxicosis with hyperthyroidism (for example, Graves' disease or toxic nodular disease) and thyrotoxicosis without hyperthyroidism (for example, transient thyroiditis) in adults by:
• measuring TSH receptor antibodies (TRAbs) to confirm Graves' disease
• considering technetium scanning of the thyroid gland if TRAbs are negative

Ultrasound for adults with thyrotoxicosis should only be considered if they have a palpable thyroid nodule

Children and young people

• differentiate between thyrotoxicosis with hyperthyroidism (Graves' disease) and thyrotoxicosis without hyperthyroidism (for example, transient thyroiditis) in children and young people by:
• measuring thyroid peroxidase antibodies (TPOAbs) and TRAbs considering technetium scanning of the thyroid gland if TRAbs are negative

Only offer ultrasound to children and young people with thyrotoxicosis if they have a palpable thyroid nodule or the cause of thyrotoxicosis remains unclear following thyroid autoantibody testing and technetium scanning.

Reference:

• (1) De Leo S, Lee SY, Braverman LE. Hyperthyroidism. Lancet (London, England). 2016;388(10047):906-918.  
• (2) Devereaux D, Tewelde SZ. Hyperthyroidism and thyrotoxicosis. Emerg Med Clin North Am. 2014;32(2):277-92  
• (3) Ross DS et al. 2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis. Thyroid. 2016;26(10):1343-1421
• (4)NICE (November 2019). Thyroid disease: assessment and management