Functional thyroid tissue producing an excess of thyroid hormone occurs in a number of clinical conditions. The major causes in humans are:

Graves disease. An autoimmune disease (usually, the most common cause with 50–80% worldwide, although this varies substantially with location- i.e., 47% in Switzerland (Horst et al., 1987) to 90% in the USA (Hamburger et al. 1981)). Thought to be due to varying levels of iodine in the diet. It is eight times more common in females than males and often occurs in young females, around 20 – 40 years of age. Toxic thyroid adenoma (the most common cause in Switzerland, 53%, thought to be atypical due to a low level of dietary iodine in this country)
Toxic multinodular goiterHigh blood levels of thyroid hormones (most accurately termed hyperthyroxinemia) can occur for a number of other reasons:

Inflammation of the thyroid is called thyroiditis. There are several different kinds of thyroiditis including Hashimotos thyroiditis (Hypothyroidism immune-mediated), and subacute thyroiditis (de Quervains). These may be initially associated with secretion of excess thyroid hormone but usually progress to gland dysfunction and, thus, to hormone deficiency and hypothyroidism. Oral consumption of excess thyroid hormone tablets is possible (surreptitious use of thyroid hormone), as is the rare event of eating ground beef or pork contaminated with thyroid tissue, and thus thyroid hormones (termed hamburger thyrotoxicosis or alimentary thyrotoxicosis). Pharmacy compounding errors may also be a cause. Amiodarone, an antiarrhythmic drug, is structurally similar to thyroxine and may cause either under-or overactivity of the thyroid.
Familial benign copper deficiency, also known as Familial benign hypocupremia is a rare genetic disorder which is characterized by hypocupremia that causes symptoms such as epilepsy, hypotonia, seborrheic skin, thriving failure and mild anemia. Radiological findings include tibia and femur spurring. Transmission is thought to be either autosomal dominant or X-linked dominant.Symptoms are caused by a familial tendency of having low levels of copper within the body and can be improved (treated and managed) with oral supplements of copper.It has been described in members of a 3-generation Hungarian family. == References ==