Subclinical hypothyroidism in childhood and adolescense.

Subclinical hypothyroidism (SH) is defined as a serum thyroid-stimulating hormone (TSH) level above the reference range with normal serum free thyroxin (sT4) and free triiodothyronine (sT3) levels. The prevalence of SH in children and adolescents is reported between 1.7% and 9.5%. Hashimoto's thyroiditis is the most prevalent cause of SH in children. Although it has been suggested that SH is entirely an asymptomatic laboratory diagnosis, typical hypothyroid symptoms as well have been reported in some patients. Results of the adult studies on SH revealed that SH had unfavorable effects on cardiovascular system (atherosclerosis); metabolic parameters (dyslipidemia, insulin resistance, etc.); neuromuscular system; and cognitive functions in the long term. The number of studies investigating the effect of childhood SH on growth, bone maturation, lipid parameters, carbohydrate metabolism, neuromuscular system, and cognitive and cardiac function is limited. Knowledge about the natural history of SH is unclear even though there are numerous studies upon this subject. In children and adults, treatment of SH with L-T₄ is still a matter of debate, and there is no consensus on this issue yet.