What are the common causes of hyperthyroidism?

Hyperthyroidism, or overactive thyroid, is commonly caused by several conditions including: 1. Nodular goiter with hyperthyroidism: multinodular toxic goiter accounts for about 10% of the causes of hyperthyroidism. This condition results from multiple autonomous nodules within the thyroid gland excessively secreting thyroid hormones. 2. Autonomous hyperfunctioning adenoma: approximately 5% of hyperthyroidism cases are caused by this condition. It involves a thyroid adenoma that autonomously secretes thyroid hormones, leading to symptoms of hyperthyroidism. 3. Iodine-induced hyperthyroidism: this form of hyperthyroidism is caused by excessive iodine intake. Although relatively uncommon, it can occur in specific situations (e.g., long-term consumption of large amounts of iodine-containing medications or foods). 4. Pituitary hyperthyroidism: also known as secondary hyperthyroidism, this is a rare condition. It occurs when the pituitary gland secretes excessive amounts of thyroid-stimulating hormone (TSH), which stimulates thyroid growth and excessive secretion of thyroid hormones.