Causes

Graves' disease is caused by a malfunction in the body's disease-fighting immune system. It's unknown why this happens.

The immune system normally produces antibodies designed to target a specific virus, bacterium or other foreign substance. In Graves' disease — for reasons that aren't well understood — the immune system produces an antibody to one part of the cells in the hormone-producing gland in the neck (thyroid gland).

Normally, thyroid function is regulated by a hormone released by a tiny gland at the base of the brain (pituitary gland). The antibody associated with Graves' disease — thyrotropin receptor antibody (TRAb) — acts like the regulatory pituitary hormone. That means that TRAb overrides the normal regulation of the thyroid, causing an overproduction of thyroid hormones (hyperthyroidism).

Cause of Graves' ophthalmopathy

Graves' ophthalmopathy results from a buildup of certain carbohydrates in the muscles and tissues behind the eyes — the cause of which also isn't known. It appears that the same antibody that can cause thyroid dysfunction may also have an "attraction" to tissues surrounding the eyes.

Graves' ophthalmopathy often appears at the same time as hyperthyroidism or several months later. But signs and symptoms of ophthalmopathy may appear years before or after the onset of hyperthyroidism. Graves' ophthalmopathy can also occur even if there's no hyperthyroidism.