What is the most common cause of hyperthyroidism?

Graves' disease is recognized as the most common cause of hyperthyroidism due to its pathophysiology involving autoimmune stimulation of the thyroid gland. In Graves' disease, the immune system produces antibodies known as thyroid-stimulating immunoglobulins (TSIs) that bind to the thyroid-stimulating hormone (TSH) receptor. This interaction results in the excessive production of thyroid hormones (T3 and T4), leading to the hypermetabolic state characteristic of hyperthyroidism.

Graves' disease is particularly prevalent, accounting for approximately 70-80% of hyperthyroidism cases. This condition often presents with symptoms including weight loss, anxiety, increased heart rate, and heat intolerance, and it can also lead to distinctive ocular manifestations known as Graves' ophthalmopathy.

While Hashimoto's thyroiditis is an autoimmune disorder typically associated with hypothyroidism, thyroid adenoma refers to benign tumors of the thyroid that can occasionally produce excess hormone but are less common overall. Thyroiditis can lead to brief hyperthyroid states, such as in subacute thyroiditis, but is not a frequent primary cause of persistent hyperthyroidism.