Causes and laboratory investigations of thyrotoxicosis

The term thyrotoxicosis identifi es the clinical syndrome caused by elevated circulating thyroid hormones of all sources, while the term hyperthyroidism includes only the disorders due to an increased secretion of hormones by the thyroid gland. Hyperthyroidism is the most frequent cause of thyrotoxicosis. Destructive processes involving the thyroid gland that induce unregulated discharge of preformed thyroid hormones (destructive thyrotoxicosis) and circulating thyroid hormone of extrathyroidal origin (exogenous or extrathyroidal thyrotoxicosis) are less common causes of thyrotoxicosis. Although careful history taking and physical examination often allows a diagnosis of thyrotoxicosis to be made, laboratory confi rmation by measurement of thyroid-stimulating hormone (TSH) and thyroid hormone is always needed. Once thyrotoxicosis is confi rmed, laboratory testing and thyroid imaging are required to identify the cause of thyrotoxicosis.