HYPOTHYROIDISM

a deficiency in available thyroid hormone secreted by the thyroid gland. Hypothyroidism may be caused by any of a number of factors, including inadequate iodine intake (iodine being a key constituent of thyroid hormone); a defect in the synthesis of thyroid hormone; excessive intake of agents that block iodine metabolism ( e.g., cobalt, resorcinol, cyanate); inborn errors of metabolism; inadequate secretion of thyroid stimulating hormone from the anterior pituitary; and thyroid antibodies (autoimmunity). If the thyroid gland grows abnormally large, in an attempt to compensate for iodine lack, the condition is termed endemic, or colloid, goitre. If the gland underfunctions from birth or infancy and there is no compensatory treatment, the result is cretinism, or juvenile myxedema; if the inadequacy occurs later in life, the condition is myxedema. Hypothyroidism is treated by replacement therapy using synthetic or natural thyroid hormones. See cretinism; myxedema.