116 A grave affair-an unusual case of congenital thyrotoxicosis in a preterm baby caused by transplacental passage of maternal thyroid stimulating hormone antibodies during pregnancy

Abstract

<h3>Introduction</h3> Congenital hyperthyroidism is a rare disease that can affect infants born to mothers with Graves disease. Thyroid stimulating hormone receptor antibodies (TRAb) cross the placenta and can cause foetal and neonatal thyrotoxicosis. This can have implications on foetal growth and may cause intra uterine growth restriction as well as cardiovascular complications such as foetal tachycardia. Postnatally signs of hyperthyroidism may include tachycardia, hypertension, irritability and poor weight gain. This case illustrates how high maternal TRAb led to foetal thyroid stimulation and thus foetal and neonatal thyrotoxicosis. It also demonstrates the difficulties encountered in managing the affected baby after birth. <h3>Report</h3> Baby was born at 34+3 weeks. Maternal history of Graves disease for which mother underwent a thyroidectomy 5 years previously. She was on thyroxine replacement. Mother was euthyroid during pregnancy. Foetal tachycardia was noted from 20 weeks gestation and the thyroid gland showed increased vascularity on antenatal scans. Baby also had a VSD and mild ventriculomegaly. During this time maternal TRAb was measured at &gt;30(upper normal range &gt;0.4). Carbimazole was started at 26 weeks, resulting in improvement of foetal tachycardia. Baby was born in good condition weighing 1540g (&lt;2nd centile). After birth baby was constantly jittery, irritable and tachycardic. Innitial TRAb was raised at 27.5 and TSH was &lt;0.02. After liaising with a tertiary unit paediatric endocrine team, the baby was started on propranolol and then carbimazole. Symptoms of thyrotoxicosis improved after starting treatment and after 2 weeks baby was discharged from our neonatal unit. Thyroid function as well as TRAb were monitored closely and propranolol and then carbimazole were discontinued by 1 month. Baby has since needed thyroxine replacement therapy, and continues to be closely monitored and managed by the local paediatric team in close cosultation with the tertiary paediatric endocrine unit. <h3>Conclusion</h3> This is a rare case of fetal and neonatal thyrotoxicosis. It demonstrates that despite maternal treatment with thyroidectomy and the mother being euthyroid during pregnancy, transplacental passage of TRAb can cause thyrotoxicosis in the foetus and later on the neonate. Although such cases are rare they have a relatively high mortality and morbidity. It shows the significant implications on the baby’s growth and cardiovascular compromise that may occur with thyrotoxicosis in the newborn. In addition it highlights the complex management of this group.