Natural history of subclinical hypothyroidism in children and adolescents

Diagnosis of subclinical hypothyroidism (SH) is based on interpretation of biochemical tests in the absence of the evident clinical symptoms. Mildly elevated TSH with normal fT₄ are common in adults and the prevalence of this finding is reported to be 1-10% of general population, being higher in the elderly. In pediatric population its prevalence is lower than 2%. Moreover in about 60% of subjects the natural course of SH is a reversal of the elevated TSH to normal values. Only 3% of them progress to overt hypothyroidism with TSH values above 10 mUI/l. The risk of progression is higher in patients with elevated anti-thyroid antibodies and higher degree of hypoechogenicity at thyroid ultrasound. Increased prevalence of SH is described in obese and overweight subjects, children with Down’s syndrome, with diabetes type 1 and in girls with Turner’s syndrome. Studies regarding the natural history of SH and its consequences in children are scarce and their conclusions are controversial. Meta-analysis of 39 potentially relevant articles showed that SH in children seems to be a remitting process with a low risk of progression toward overt hypothyroidism regardless of the L-T ₄ treatment. There was also no clear evidence of the beneficial effect of L-T₄ treatment on psychological and physical development. Replacement therapy did not seem to be justified in children with SH and TSH values between 5 -10 mUI/l, no goiter and negative anti-thyroid antibodies. Therefore decision regarding the treatment of the young patient with elevated TSH but normal fT₄ value continues to be controversial.