Hyperthyroidism is an excess of thyroid hormone resulting from overactivity of the thyroid gland. It speeds up processes in the body and may cause symptoms such as nervousness, tremor, sudden weight loss, rapid heartbeat and thyroid enlargement (goiter).

In some cases, hyperthyroidism also affects the eyes and the skin, particularly on the shins and feet. Potential complications of hyperthyroidism include heart problems and osteoporosis.

Several disorders can cause hyperthyroidism. They include:

• Graves' disease. An autoimmune disorder in which antibodies stimulate the thyroid to produce too much thyroid hormone.
  
  
• Hyperfunctioning thyroid nodules. Occurs when lumps in the thyroid, which are generally noncancerous, produce too much thyroid hormone.
  
  
• Thyroiditis. Inflammation and temporary destruction of the thyroid gland, which can allow excess hormones to leak into the bloodstream.

Diagnosing hyperthyroidism can be difficult because symptoms may mimic those of other conditions. A physical examination often reveals signs and symptoms such as eye problems or brittle hair. Thyroid blood tests aid in diagnosis.

Treatment options include radioactive iodine taken in pill or liquid form to shrink the thyroid gland. Antithyroid medications and surgery also may be used. Some therapies affect the thyroid gland so significantly that patients may develop hypothyroidism (underactive thyroid) and have to take hormonal supplements.