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Hyperthyroidism is a condition in which the thyroid gland is making too much thyroid hormone. When the body’s cells are exposed to too much thyroid hormone they become overactive. They burn up energy too quickly, and release too much heat. This results in the typical symptoms of hyperthyroidism, which include:


Complications of Other Diseases

There are a number of diseases that can cause hyperthyroidism. The most common is called Graves’ disease. Graves’ disease was first described by Dr. Robert Grave in 1835. It belongs to a group of diseases that we don’t understand very well called autoimmune diseases. These are diseases in which the body’s immune system attacks one of the body’s own parts. In Graves’ disease, the attack of the immune system is on the thyroid gland. This attack stimulates the gland to make too much thyroid hormone.

Renegade cells

Some patients are born with a few cells in the thyroid gland that make thyroid hormone without any stimulation from the pituitary gland. Sometimes as these patients get older, the thyroid gland becomes large and develops more and more of these cells. The thyroid makes more and more thyroid hormone until, eventually, the patient develops hyperthyroidism. This is called a toxic multinodular goiter. It is more common in older individuals.


Some patients develop a benign tumor in the thyroid gland that makes thyroid hormone without being stimulated by the pituitary gland. If the tumor grows large enough it can make enough hormone to cause hyperthyroidism.


Some patients develop an inflammation in the thyroid gland called a “thyroiditis.” This can be painful, called subacute thyroiditis, or it can be painless, called painless or silent thyroiditis. The inflamed thyroid gland leaks thyroid hormone into the blood stream – hormone that had previously been stored in the thyroid gland. This can expose the body to an excessive amount of thyroid hormone for 2 – 4 months. After that, the thyroid gland runs out of thyroid hormone. Since the gland is inflamed and not working correctly, the patient can then go through a period of a few months where there is too little thyroid hormone in the blood stream. These types of thyroiditis are usually self-limited, and the thyroid returns to normal after several months. This kind of thyroid disease can also develop immediately after pregnancy.

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    Last Reviewed: Mar 25, 2013

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    Associate Professor of Medicine

    School of Medicine

    Case Western Reserve University