Background: An increase in the incidence of congenital hypothyroidism (CH) with a normally located gland has been reported worldwide. Affected individuals display transient or permanent CH during follow-up in childhood. We aimed to determine the prevalence of transient CH and to assess the possibility of distinguishing between transient and permanent CH in early infancy.
Methods: This observational cohort study included all patients identified by systematic neonatal screening for CH in the northern Parisian region between 2002 and 2012 and treated for CH with a normally sited gland. A standardized data collection form was completed prospectively at diagnosis. Patients were classified, during the follow-up, as having transient or permanent CH.
Results: Of the 92 patients initially treated for CH with a normally located gland during the neonatal period, 49 (54%) had a transient form of CH after the cessation of levothyroxine treatment at 1.5 (0.63.2) years of age. Multivariate analysis revealed that transient CH was associated with a lower likelihood of having a family history of CH (P=0.03) and a lower levothyroxine dose at six months of age (P=0.03) than permanent CH. Sex, ethnicity, neonatal problems, such as prematurity, being small for gestational age and/or neonatal distress, iodine status, coexisting malformations, initial CH severity and thyroid morphology at diagnosis had no effect. Receiver operating characteristics curve analysis showed that a cutoff of 3.2 μg/kg/d for levothyroxine dose requirement at six months of age had a sensitivity of 71% and a specificity of 79% for predicting transient CH, with values below this threshold considered predictive of transient CH.
Conclusion: In patients with CH and a normally sited gland, these findings highlight the need to evaluate levothyroxine dose requirement early, at six months of age, particularly in patients with no family history of CH, for early identification of the approximately 50% of patients for whom treatment should be stopped. Parents should be made aware, when they are informed of their childs diagnosis during the neonatal period, that subsequent re-investigation will be necessary to determine whether the CH is persistent during childhood. However, the natural course of thyroid function of patients with transient CH during early childhood remains to be determined, and it is unknown whether these patients need to resume L-T4 treatment later in life during times of increased thyroxine need due to increases in metabolism, such as puberty and pregnancy.
27 - 29 Sep 2018
European Society for Paediatric Endocrinology