In most of the cases hyperthyroidism is due to a problem in thyroid itself. The conditions include:

  • Grave’s disease or diffuse toxic goiter is the most common cause of hyperthyroidism. Diffusely enlarged thyroid gland and the presence of antibodies (Thyroid stimulating immunoglobulin) are characteristics of this autoimmune (where the defense mechanism of the body tends to act against its own thyroid gland) disorder. It is much more common in women and usually seen in the age group of 20-50 years.
  • Plummer’s disease is a condition in which one (nodular toxic goiter) or more (toxic multinodular goiter) lumps in the gland may become overactive. These nodules are nothing but areas of abnormal tissue growth within the thyroid gland, which escape the mechanism that normally control the thyroid gland and produce thyroid hormone in large quantities. It usually affects older people.
  • Subacute thyroiditis (De Quervain’s thyroiditis): The cause is commonly believed to be viral. The thyroid inflammation that follows may lead to destruction of thyroid cells resulting in release of thyroid hormones. This may cause temporary periods of hyperthyroidism (Thyrotoxicosis). It is characterized by a moderately enlarged and tender (pain on pressure) thyroid. Constitutional symptoms (such as body ache, general feeling of being unwell) which are typical of a viral illness may also be present. In certain cases tenderness is absent and then it is known as “silent thyroiditis”.
  • Jodbasedow disease or iodine induced hyperthyroidism may occur in people taking large amounts of iodine in the diet or in the form of radiographic contrast materials or drugs especially amiodarone.
  • Factitious Hyperthyroidism: It is caused by excessive consumption of exogenous (external source) thyroid hormones. Over medication in hypothyroidism or consumption of meat contaminated with animal thyroid (hamburger toxicosis) may cause this condition.
  • Other rare causes include:
    • excess TSH production by pituitary tumors
    • a condition called as struma ovarii in which thyroid tissue is contained in the teratoma (type of tumor) of ovary. This thyroid tissue may secrete thyroid hormones on its own.