What are the causes of hyperthyroidism/thyrotoxicosis?
Primary hyperthyroidism due to excessive production of thyroid hormone due to thyroid overactivity: • Graves’ disease is the most common cause of hyperthyroidism. It is an autoimmune disorder in which antibodies are directed against the thyroid-stimulating hormone (TSH) receptor. These antibodies mimic the effects of TSH produced by the pituitary gland, stimulating thyroid growth and function and causing a toxic diffuse goitre. A clinically apparent ophthalmopathy occurs in 25–50% of people [Cooper, 2004; Reid and Wheeler, 2005]. • Toxic multinodular goitre is the second most common cause of hyperthyroidism in the UK [BTA et al, 2006]. This occurs in a thyroid gland with at least two autonomously functioning thyroid nodules that secrete excess thyroid hormone, producing typical signs and symptoms of hyperthyroidism. • Toxic thyroid nodule (adenoma) probably accounts for no more than 5% of cases of hyperthyroidism. The nodule produces enough hormone to suppress secretion of TSH from the
