Graves' disease is an autoimmune condition that is the primary cause of hypothyroidism. In addition to the typical symptoms of that condition, it also presents with goiter, mood disorders and a distinctive bulging of the eyes known as Graves' opthalmopathy. Its underlying cause is unknown, but its etiology is well understood - the antibodies that attack the thyroid induce it to produce more thyroid hormones. It is far more common in women than men, and seems to have a genetic component. It is a frequent differential diagnosis on the show, but no patient has yet been diagnosed with the condition.
Because of the importance of thyroid hormones, treatment of the disease is difficult. Mild cases can often be treated with beta blockers, which alleviate the symptoms of high thyroid levels such as tachycardia and nausea. The next stage of treatment are drugs that suppress the production of the hormone. However, when this treatment fails, radioactive iodine is used to destroy a part of the thyroid. If this fails, the final intervention is surgical removal of the thyroid followed by hormone replacement treatment.