MON-582 The Natural History of Delayed TSH Elevation in Neonatal Intensive Care Newborns

Context: Delayed TSH elevation (dTSH) is defined as elevated TSH in the second neonatal screen following normal TSH in the initial screen. The clinical outcome of newborns with dTSH is not entirely elucidated, although several studies have suggested a full recovery in most cases. Objective: We aim to elucidate the natural history of dTSH in a group of neonatal intensive care newborns. In addition, we aim to define clinical and endocrine parameters that may predict the outcome of newborns with dTSH, i.e. transient vs. permanent hypothyroidism. Design, setting and participants: An observational study was performed in a cohort of 113 children with a history of dTSH. Birth parameters, thyroid screening results, thyroid gland imaging, levothyroxine dose and neurological outcome were compared between newborns with spontaneous recovery and children with a final diagnosis of either transient of permanent hypothyroidism. Results: 93% of the children with a history of dTSH demonstrated a recovery, either spontaneously or following levothyroxine treatment (transient hypothyroidism). Newborns with a spontaneous recovery demonstrated milder thyroid dysfunction on the newborn screening compared with newborns who started levothyroxine treatment. Levothyroxine dose was lower in children with transient vs. permanent hypothyroidism only during the first six months of life, but otherwise these groups were similar in birth parameters, thyroid screening tests and gland imaging. In spite of similar management, developmental delay was more common in children with permanent than transient hypothyroidism (71% vs. 17%, p=0.01). Duration of treatment was highly variable in children with transient hypothyroidism and ranged from several months to over three years. Conclusion: Thyroid dysfunction is transient in most cases of dTSH. No reliable parameters can predict a-priori transient vs. permanent hypothyroidism, but the neurological outcome in the latter form is worse. A prospective study is required to define the earliest timing for a safe cessation of therapy in newborns with dTSH.