What is the most common cause of hyperthyroidism?

Graves disease is recognized as the most common cause of hyperthyroidism due to its autoimmune nature that stimulates the thyroid gland to produce excessive amounts of thyroid hormones. In Graves disease, autoantibodies activate the thyroid-stimulating hormone (TSH) receptor, which leads to an increase in hormone synthesis and secretion. This results in elevated levels of thyroxine (T4) and triiodothyronine (T3), causing the symptoms associated with hyperthyroidism, such as increased metabolism, weight loss, anxiety, and heat intolerance.

While other conditions listed can cause hyperthyroidism, they are less prevalent than Graves disease. A toxic uninodular goiter can cause hyperthyroidism, but it is typically a secondary cause that occurs in a localized area of the thyroid gland rather than having the widespread autoimmune effect seen in Graves disease. Subacute thyroiditis, which usually follows a viral infection, often leads to temporary hyperthyroidism but is not a chronic condition and generally self-limiting. A pituitary tumor can lead to hyperthyroidism through excess hormone production, but this is quite rare compared to the autoimmune mechanism of Graves disease. Therefore, the distinction of Graves disease as the most common cause of hyperthyroidism stands clear