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Background Long-term consequences of mild subclinical hypothyroidism (SH) in children are still unclear, and the need for levothyroxine (L-T4) supplementation remains controversial. We designed a 2-year, case-control, prospective study of a cohort of children with SH to evaluate the effects of L-T4 therapy on neurocognitive outcome. Methods Thirty-four children, age 9.1 ± 2.6 years, with long-lasting, idiopathic, and mild SH, and 34 healthy matched controls, were enrolled. Twenty SH children underwent a 2-year L-T4 treatment (group A), whereas 14 refused treatment and were reevaluated after a 2-year-follow-up (group B). IQ and specific cognitive domains were evaluated in all children at study entry and after 2 years of therapy (group A) or observation (group B) in SH individuals. Results In SH children baseline IQ scores were normal and comparable to controls (full-scale IQ [FSIQ] 100.4 ± 11.3 vs 101.8 ± 14.2, verbal IQ [VIQ] 99.7 ± 13.7 vs 98.3 ± 14.9 and performance IQ [PIQ] 101.2 ± 10.4 vs 105 ± 10.4). In group A, L-T4 treatment was associated with normalization of thyrotropin (6.3 ± 1.0 mIU/L at baseline vs 2.8 ± 1.4 mIU/L at 2 years, P Conclusions Our data suggest neurocognitive function in children is not impaired by persistent, mild, untreated SH and is not significantly modified by 2-year L-T4 supplementation.

ObjectiveThe treatment of children with subclinical hypothyroidism (SH) is controversial for TSH values between 4.5 and 10 mU/l. The aim of this cross-sectional, controlled study was to evaluate growth and intellectual outcome in children with persistent SH who have never been treated with levothyroxine.Design and methodsClinical and auxological parameters, thyroid function, and intellectual outcome were evaluated in 36 children with persistent SH at the age of 9.7±0.6 (range 4–18.0) years. Children had been followed longitudinally for 3.3±0.3 (range 2.0–9.3) years, from first diagnosis of SH until enrollment in the study. Thirty-six age- and sex-matched children were enrolled in the study as controls.ResultsAt study entry, height (−0.8±0.2 SDS), bone age/chronological age (BA/CA ratio 0.92±0.6), and body mass index (BMI −0.1±0.2 SDS) in SH children were normal. Despite long-term duration of SH, none of these parameters showed a worsening with respect to height (−0.7±0.2 SDS), BA/CA (0.97±0.03), and BMI (−0.1±0.2) at the time of first SH detection. None of the children showed overt signs or symptoms of hypothyroidism during the follow-up.Verbal (99.1±2.2), performance (100.4±1.9), and full-scale (99.7±1.9) intelligence quotient (IQ) scores in SH children were normal and comparable to those of controls. No relationship was detected between IQ scores and the degree or duration of SH.ConclusionsPersistent SH in children is not associated with alterations in growth, bone maturation, BMI, and cognitive function or other complaints that could be ascribed to SH even after several years without therapeutic intervention.