Hyperthyroidism occurs when the thyroid gland produces too much thyroid hormone, leading to an acceleration of the body’s metabolism and various physiological effects. The causes of hyperthyroidism are diverse, involving autoimmune conditions, thyroid gland abnormalities, inflammation, hormone intake, and rare tumors.
The most common cause of hyperthyroidism is **Graves’ disease**, an autoimmune disorder. In Graves’ disease, the immune system mistakenly produces antibodies that stimulate the thyroid gland to produce excess thyroid hormones. This overstimulation causes the gland to enlarge and become overactive, resulting in symptoms such as rapid heartbeat, weight loss, and nervousness. Graves’ disease is unique because it directly involves the immune system attacking the thyroid, causing it to function abnormally[1][3].
Another major cause is **toxic multinodular goiter**, also known as Plummer disease. This condition often develops over many years, especially in areas with iodine deficiency. The thyroid gland initially enlarges due to constant stimulation by thyroid-stimulating hormone (TSH), but over time, certain nodules within the gland begin to function independently, producing excess thyroid hormones without regulation. This leads to hyperthyroidism, typically in older adults[1].
A related cause is a **toxic adenoma**, which is a benign tumor of the thyroid gland. These tumors can have mutations in the TSH receptor gene, causing the tumor cells to produce thyroid hormones autonomously, independent of normal regulatory signals. This results in localized overproduction of thyroid hormones and hyperthyroidism[1].
Certain types of **thyroiditis**, or inflammation of the thyroid gland, can also cause hyperthyroidism, though usually temporarily. For example, **silent lymphocytic thyroiditis** often occurs after pregnancy and causes the release of stored thyroid hormones into the bloodstream. Another form, **subacute granulomatous thyroiditis**, is painful and causes inflammation that leads to hormone leakage. In these cases, hyperthyroidism is usually mild and self-limiting, lasting only until the hormone stores are depleted[1].
Excessive intake of thyroid hormone, either prescribed or from supplements, can cause hyperthyroidism as well. Some people take thyroid hormone preparations to treat hypothyroidism or to reduce goiter size, but overdosing can lead to an overactive thyroid state. Additionally, unregulated thyroid hormone supplements sold in health stores may contain variable amounts of hormone, causing unpredictable effects and hyperthyroidism[1].
Rare causes include **thyrotropin-secreting tumors of the pituitary gland**, which produce excess TSH and overstimulate the thyroid, and **struma ovarii**, a rare ovarian tumor containing thyroid tissue that produces excess hormone[1].
In children and adolescents, hyperthyroidism is most commonly caused by autoimmune factors similar to Graves’ disease. Genetics, environmental triggers, and immune system dysfunction all contribute to the development of hyperthyroidism in younger populations. These factors interact in complex ways, making the exact cause difficult to pinpoint but clearly involving immune system abnormalities[2].
Overall, hyperthyroidism results from conditions that cause the thyroid gland to produce too much hormone either by overstimulation, autonomous hormone production, inflammation, or external hormone intake. The thyroid gland, a butterfly-shaped organ in the neck, regulates metabolism, heart rate, body temperature, and many other vital functions, so excess hormone production speeds up these processes, leading to the characteristic symptoms of hyperthyroidism[4][5].
