Box 3.13Causes of hyperthyroidism

Common

• Graves' disease (~80%) — autoimmune with stimulating antibodies to the TSH receptor.
• Toxic multinodular goitre (~ 15%).

Uncommon

• Toxic adenoma (‘hot’ nodule, ~ 2%).
• Thyroiditis (~ 1%).

Rare

• TSH secreting pituitary tumor (<0.01%) — biochemically this must be distinguished from thyroid hormone resistance when TSH secretion is high due to loss of negative feedback effects.
• Trophoblastic tumors (<0.001%) — high concentrations of the homologous chorionic gonadotrophin hormone interacting with the TSH receptor.
• Thyrotoxicosis factitia (<1%) — excess thyroxine ingestion in patients who perceive weight loss and other benefits.
• Thyroid follicular carcinoma (<0.01%).