Thyroid definitions Acquired hypothyroidism: it occurs when the thyroid at some point stops working properly and produces fewer hormones. It is a relatively common condition. Autoimmune: diseases due to abnormal immune response that attacks the cells and tissues of its own body. Autoimmune thyroiditis. Most common form of thyroiditis due to a reaction of the immune system that destroys the cells that produce thyroid hormones. Congenital hypothyroidism. It occurs when the thyroid is not present at birth. Hashimoto’s thyroiditis. Synonymous with autoimmune thyroiditis. It is named after the American physician of Japanese descent who first described it over a century ago. Hyperthyroidism. Situation in which the thyroid gland 'works too much' and causes agitation, insomnia, accelerated rhythm of the heartbeat and weight loss. Pituitary. Gland located within the brain that regulates various body functions among which, through the hormone TSH, thyroid function. Subclinical thyroiditis. Autoimmune thyroiditis in a mild form in which clinical symptoms are not present. TSH. Hormone produced by the pituitary, regulates the function of the thyroid.