Hashimoto thyroiditis is a chronic inflammation of the thyroid gland. The thyroid gland is in the front of the neck just below the Adam's apple. It secretes thyroid hormone, which is important in metabolism throughout the body.
Hashimoto thyroiditis is considered an autoimmune disease. This means that a person's immune system attacks his or her own body. No one knows why this happens. With this disease, the immune system attacks the thyroid gland. This can cause thyroid hormone imbalances. Hashimoto thyroiditis is one of the most common causes of a low thyroid hormone level, called hypothyroidism.
The exact cause of Hashimoto thyroiditis is not known. As with all autoimmune disorders, the immune system abnormally attacks the body. Hashimoto thyroiditis also occurs more often in people who have other autoimmune disorders and diabetes.