This disease is called Graves' disease. There is usually no pain in the thyroid gland. In most cases, it is uncertain what triggers this immune system attack. However, some individuals seem predisposed to this disease because thyroid problems run in their family. In addition, some individuals report the onset of Graves' disease during periods of stress, which is known to affect immune system function.
Hyperthyroidism also occurs in other situations.
In the elderly it may be caused by an enlarged, lumpy thyroid gland called a toxic nodular goiter. Usually such individuals have had a goiter for several years and the increased thyroid activity has developed very slowly. Women who have just had a baby are also prone to hyperthyroidism. This form is called postpartum thyroiditis. In other individuals, a viral infection in the thyroid gland can cause a disease called subacute thyroiditis, which is one of the very few conditions that causes pain in the thyroid gland.