[Transient neonatal hyperthyroidism caused by transplacental transport of pituitary TSH receptor antibodies]

Neonatal hyperthyroidism is a relatively rare condition. It can be severe and difficult to treat when the maternal hyperthyroidism has recently been recognized.

A baby was born at 37 weeks of gestational age to a mother whose hyperthyroidism was only suspected at the 34th week. The mother was not given propylthiouracil until the day before delivery. At birth, the newborn presented with meconial fluid; it weighed 2,380 grams, was 46 cm long and had a head circumference of 32 cm. Clinical examination showed exophthalmos, tachycardia, hepatosplenomegaly, restlessness, moderate goiter and premature craniosynostosis. Laboratory data showed elevated serum free T4 (76 pmol/l), unmeasurable TSH, and the presence of thyroid-stimulating immunoglobulins. The infant was given propranolol (10 mg/day), and carbimazol (3.75 mg/day) from day 13. Clinical and biological improvement allowed the carbimazol to be stopped at 1 month. A relapse was treated with carbimazol plus L-thyroxine. Both drugs were discontinued at the age of 4 months. At 12 months, the baby is perfectly well and has developed normally.

This transient thyrotoxicosis was due to the transplacental passage of TSH receptor antibodies. Its management was difficult because the mother was treated late during her pregnancy.