[Thyroid disorders in childhood and adolescence. Part 2: Hypothyroidism].

Hypothyroidism is the most frequent thyroid dysfunction. It is the consequence of a decrease in the biological activity of thyroid hormones in target tissues. The aim of this paper is to review and update acquired hypothyroidism in childhood and adolescence with emphasis on primary hypothyroidism due to its greater frequency. Hashimoto's thyroiditis, also known as chronic lymphocytic thyroiditis, is the most common cause of primary acquired hypothyroidism. The distinctive feature is the profound impact on skeletal growth, maturation, and pubertal development, with potential implications on adult height. Signs and symptoms of acquired hypothyroidism are similar to those reported in adults and are generally not associated with neurodevelopmental impairment. Biochemical confirmation of primary hypothyroidism requires the finding of elevated thyrophine and decreased free thyroxine levels. Treatment goals are to achieve normal growth and maturation as well as cognitive development. In most of the patients, replacement treatment reverses symptoms and signs of hypothyroidism and may decrease goiter size.