TSH is a hormone produced by the pituitary gland. If the TSH test level is high as in hypothyroidism, the body is not producing enough thyroid hormone and the pituitary gland is encouraging it to produce more. If TSH levels are below normal, the pituitary gland is signaling that there is too much thyroid hormone in the circulation as in hyperthyroidism. As the damaged thyroid gland produces less hormone, the pituitary gland secretes thyroid-stimulating hormone to encourage the thyroid to work harder. This increased demand on the thyroid may cause it to enlarge, creating what is commonly known as a goiter.
Hypothyroidism can begin and progress slowly.
At first, the person may experience mild or no symptoms. In later stages, signs may be mistaken for other health conditions. The risks of not treating the problem differ. In newborns, prompt treatment is crucial in preventing mental retardation, delayed growth and other severe abnormalities. Children and adolescents are also at risk of abnormal mental and physical development.