Subclinical hypothyroidism in children and adolescents: a wide range of clinical, biochemical, and genetic factors involved

Subclinical hypothyroidism in children: normal variation or sign of a failing thyroid gland?

Subclinical hypothyroidism (SCH), defined by a normal total or free T4 level and a mildly elevated TSH (typically 5–10 mU/L), is common in children, but there is currently no consensus on management. Several recent pediatric studies indicate that progression of SCH to overt hypothyroidism (OH) is uncommon and that over a period of several years, elevated TSH usually either normalizes or persists but does not increase. The etiology appears to be multifactorial, with some cases representing minor developmental abnormalities, some related to obesity, some to mild autoimmune thyroiditis, and some associated with mutations in the gene for the TSH-receptor. There are no pediatric studies showing clinical benefit of treating these children with thyroid hormone, but additional studies in this area are needed. Since few cases of pediatric SCH progress to OH, treatment can be deferred, and periodic follow-up testing may be the preferred strategy, with elevated thyroid antibodies or a goiter being considered risk factors for eventual OH.

How should we manage patients with mildly increased serum thyrotrophin concentrations?

A mildly increased serum thyrotrophin (TSH) is usually because of mild thyroid failure, and the most common aetiology in iodine-replete communities is chronic autoimmune thyroiditis. It is more common in women, and the prevalence increases with age in both men and women and is associated with the presence of antithyroid antibodies. The majority will have serum TSH levels between 5-10 mIU/l, normal free thyroxine (T4) levels and relatively few symptoms. In 2004, US evidence-based consensus guidelines concluded that there were no adverse outcomes of a mildly increased serum TSH other than a risk of progression to overt hypothyroidism and few data to justify levothyroxine therapy. There is still debate as to what constitutes an increased serum TSH, particularly in older subjects. Although some subjects will progress to overt hypothyroidism, recent data suggest a significant proportion revert to a serum TSH within the reference range without treatment. Two recent meta-analyses have suggested that the possible cardiovascular risks may be more significant in younger adults. Other data suggest that mild thyroid failure may be the only reversible cause of left ventricular diastolic dysfunction. No appropriately powered prospective, randomized, controlled, double-blinded interventional trial of levothyroxine therapy for a mildly increased serum TSH exists. However, treatment in subjects who are symptomatic, pregnant or preconception, aged less than 65 years and older subjects with evidence of heart failure appear justified.