Like Hashimoto's disease, Graves' disease is an autoimmune disease, a condition caused by an immune system that mistakenly attacks its own healthy tissue. In healthy people, the immune system is on duty 24/7, always on the lookout for invaders like bacteria and viruses that threaten your health. When an invasion occurs, your immune system generates antibodies that attack the invaders, called antigens. The white blood cells work feverishly to destroy the invaders and bring about healing.

When someone has an autoimmune disease, these white blood cells are mysteriously summoned for no apparent reason, and the body treats normal healthy tissue as something foreign. The body then begins to produce antibodies against the perceived invader. Antibodies produced in an autoimmune disease are known as autoantibodies.

In people with Graves' disease, the most common antibodies are the TSI antibodies and the TPOAb. TPOAb are the same antibodies that cause Hashimoto's disease, which was discussed in Chapter 6. Graves' disease was named after Robert Graves, an Irish doctor who first identified the condition in three of his patients in early 1835.

An autoimmune attack can occur in various organs and body systems, each causing its own disease and constellation of symptoms. In Graves' disease, your thyroid is the organ under siege. As a result of this autoimmune attack, your thyroid is enlarged and churning out way too much thyroid hormone, producing the symptoms you know as hyperthyroidism. The enlargement of the thyroid gland has earned the disease the name of diffuse toxic goiter.

Unlike Hashimoto's disease, Graves' is less common and occurs in about 1 percent of the U.S. population. The condition is eight times more common in women than men and is more likely to occur in adults in their thirties and forties. The disease is much less common in adults over age fifty.