Subclinical Hypothyroidism in Children: Normal Variation or Sign of a Failing Thyroid Gland?

Primary care physicians and pediatric endocrinologists frequently face the decision of what to do about the child who has a normal total or free T4 level and a slightly elevated TSH (typically 5–10？mU/L), a situation usually referred to as subclinical hypothyroidism (SCH) [1]. The reasons for ordering the tests in the first place vary, but many primary care physicians believe that prompt evaluation and treatment are essential. The response of pediatric endocrinologists may range from a decision to start thyroid hormone immediately after confirmation of the elevated TSH, to recommending frequent monitoring of TSH for prolonged periods, to the suggestion that unless a follow-up test shows a further significant rise in TSH or a subnormal free T4, no action should be taken.There are several reasons for this lack of consensus among pediatric endocrinologists. First, there have been until recently a scarcity of studies reporting on the natural history of SCH in children; thus there has been concern that if untreated, SCH will frequently progress to overt hypothyroidism (OH). OH will be defined here as a low total or free T4 with a TSH of >20？mU/L, which all clinicians would agree requires treatment, though occasionally one encounters a clearly low free T4 with a TSH in the 10–20？mU/L range. There are no controlled pediatric studies (as there are in adults) looking at outcomes of children with SCH treated with l-thyroxine versus those given placebo. Furthermore, there is a high risk of developmental delay in infants who have untreated severe congenital hypothyroidism (low T4 and TSH usually >100). Since many children with SCH are identified during newborn screening or during the first year of life, physicians may be concerned that failing to treat SCH will expose the child to the risk of developmental delay if OH develops later or that treatment is needed to prevent growth retardation [1].The cost implications of the decision to treat or not to treat an individual child wi