Background: The prevalence of hyperthyroidism in pregnancy is about 0.2%, mostly due to Graves disease. Neonatal autoimmune hyperthyroidism caused by the transplacental passage of stimulatory thyrotropin receptor antibodies (TRAB) of the IgG class is a rare disorder. It occurs in only 2% of the neonates of mothers with Graves disease, is transient and associated with high morbidity and mortality rates up to 25%. Antithyroid drugs are the treatment of choice for neonates and premterm neonates with hyperthyroidism.
Case Report: We report the rare case of a preterm neonate born at 28+5 weeks of gestational age with a birth weight of 1580 g. After a few days the boy became irritable and developed tachycardia. At the 6th day of life the laboratory investigations revealed hyperthyroidism with suppressed serum TSH-levels, elevated fT4-levels and positive TRABs. Under treatment with propranolol and methimazole the fT4 serum levels declined to the lower limit of the normal range, so that an additional supplementation with levothyroxine was initiated. Methimazole was stopped after 3 months when TRABs were negative. The TSH serum levels remained very low for 6 months while fT4 was constantly in the normal range under treatment with levothyroxine. Eventually the levothyroxine dose was reduced and the patient became euthyroid without treatment. Serious side effects under treatment with methimazole such as neutropenia or elevated liver enzymes did not occur.
Conclusions: Although neonatal hyperthyroidism due to maternal TRABs is rare, thyroid function has to be monitored in all neonates born from mothers with Graves disease. Once hyperthyroidism is diagnozed antithyroidal treatment has to be started. Prematurity is not a contraindication for the use of antithyroidal drugs. The treatment has to be monitored thoroughly because of the known serious side effects. Furthermore, the fT4 serum levels can decline rapidly in preterm neonates and additionally the serum TSH levels remain suppressed for months. To avoid hypothyroidism intermediate treatment with levothyroxine is important.
19 - 21 Sep 2019
European Society for Paediatric Endocrinology