Conclusion: The European Society for Paediatric Endocrinology recommends an initial levothyroxine dose of 10–15 microgram /kg per day. Infants with severe disease, as defined by a very low pretreatment T4 or free T4 concentration, should be treated with the highest initial dose. Overtreatment should be avoided by careful monitoring. [2]
Postnatal thyroid hormones for preterm infants with transient hypothyroxinaemia
A systematic review by Osborn DA et al 2007 found only one eligible study providing insufficient evidence to determine whether use of thyroid hormones for treatment of preterm infants with transient hypothyroxinaemia (low T4, normal TSH) results in changes in neonatal morbidity and mortality or reductions in neurodevelopmental impairments.[23] (LOE I)
Thyroid hormones for preventing neurodevelopmental impairment in preterm infants
A systematic review by Osborn DA 2001 that included 9 studies found no support for the use of thyroid hormones in preterm infants to reduce neonatal mortality, improve neurodevelopmental outcome or to reduce the severity of respiratory distress syndrome. [24] A subgroup analysis of data from one RCT (van Wassenaer 1997) which showed benefits in infants 24–25 weeks gestation was not pre-specified.[25-27]
Conclusion: Prophylactic thyroid hormone supplementation in preterm infants and for treatment of transient hypothyroxinaemia should only be used in the context of an adequately powered clinical trial. (LOE I GOR D)
Replacement therapy in Down syndrome
A single RCT assessed the effect of thyroxine 8 microgram /kg per day in 196 Down Syndrome infants with normal newborn congenital hypothyroidism screening.[28, 29] Thyroxine-treated children had a smaller delay in motor developmental age (−0.7 months, 95% CI −1.4 to 0), but not mental developmental age (−0.7 months, 95% CI −1.5 to 0.2) at 24 months. Levothyroxine-treated children had greater gains in length (1.1 cm, 95% CI 0.2 to 2.0) and weight (378 g, 95% CI 55 to 701). However, at a mean age of 10.7 years, 123 infants were assessed as having no difference in mental or motor development, communication skills or fine-motor coordination. Levothyroxine-treated children had a larger HC (50.4 vs 49.8 cm, P 0.04) and tended to be taller (133.2 vs 131.1 cm, P0.06). The differences were greater in children with TSH ≥5 IU/L (HC: levothyroxine50.5 vs placebo 49.7 cm, P 0.01; height: levothyroxine133.8 vs placebo 130.8 cm, P 0.02), but were not found in children with TSH <5 mIU/L.
Conclusion: Administration of levothyroxine to young children with DS to stimulate general mental or motor development later in life cannot be recommended. However, levothyroxinetreatment may increase growth, especially in children with elevated neonatal plasma TSH concentrations.[28] LOE II GOR D
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