Hyperthyroidism is a condition in which overactivity of the thyroid gland causes too much thyroid hormone to build up in the bloodstream. As a result, processes in the body speed up. Left untreated, hyperthyroidism can have serious health consequences.

The thyroid gland sits just below the Adam's apple in the neck. It secretes hormones that regulate a person's metabolism, the physical and chemical processes necessary for the maintenance of life. Thyroid hormones help to:

• Control the rate at which the body uses fats and carbohydrates
  
• Maintain body temperature
  
• Influence heart rate
  
• Regulate the amount of calcium in the blood

A complex chain leads to hormone production in the thyroid. The hypothalamus in the brain signals the pituitary gland to make and release thyroid-stimulating hormone (TSH). TSH causes the release of the major thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Disorders that affect the thyroid have a crucial effect on the proper release of these hormones, which may alter a person's metabolism and potentially lead to significant health problems.

Hyperthyroidism occurs when a person’s thyroid produces too much thyroxine. This leads to a speeding up of metabolism that can result in many different symptoms, including enlargement of the gland (goiter) and sudden unexplained weight loss. In addition, some cases of hyperthyroidism cause the eyes to bulge beyond their normal socket. Tissues and muscles behind the eyes swell, a condition known as Graves' ophthalmopathy. Hyperthyroidism also can affect the skin, particularly on the shins and feet. Redness and swelling are the most common symptoms associated with the skin.

Several complications are associated with hyperthyroidism. Some patients may develop heart problems such as rapid heart rate, atrial fibrillation (heart rhythm disorder) and heart failure (inability of the heart to circulate enough blood to meet the body's needs). Hyperthyroidism also can lead to brittle bones (osteoporosis) and fractures, as excessive levels of thyroid hormone can prevent the body from incorporating calcium into the bones. According to recent research, thyroid disease may raise the risk of glaucoma, a leading cause of blindness.

Finally, people with hyperthyroidism are at increased risk for thyrotoxic crisis. This is also known as thyroid crisis or thyroid storm. When this occurs, patients may experience a sudden intensification of their symptoms, including fever, rapid pulse and delirium.