Don't miss neonatal thyrotoxicosis - the importance of assessing an at risk baby at 7 days


Page Tristan1, Stirling Heather2, Farrall Louise3, Manjunatha Rashmi1

1 Department of Endocrinology, 2 Department of Paediatrics, 3 Department of Obstetrics, University Hospitals of Coventry and Warwickshire NHS Trust, Coventry, UK.

Background: Maternal Graves disease can lead to neonatal thyrotoxicosis due to trans-placental passage of maternal activating TSH receptor antibodies.

Clinical Case: This 31 year old lady presented following a 3 year history of neck swelling, palpitations, sweating and heat intolerance. She had previously been managed abroad with carbimazole though the details were not known. Examination revealed a diffusely enlarged goitre, exophthalmos and lid lag. Blood results were in keeping with thyrotoxicosis with a TSH of <0.02mU/L, free T4 of 77.7pmol/L and free T3 of 24.6pmol/L. The patient reported to be pregnant and was at around 6 weeks of gestation. TSH receptor antibodies were markedly raised at 28.8U/l (<1.0U/l). She was managed with antithyroid medication propylthiouracil in the first trimester followed by a titrated dose of carbimazole throughout the rest of pregnancy with gradual improvement in her thyrotoxicosis symptomatically and biochemically.

Due to the markedly elevated maternal TSH receptor antibody titre, a neonatal alert was raised for the paediatricians. Antenatal ultrasonography demonstrated foetal goitre but no evidence of foetal hyperthyroidism. After delivery, neonatal thyroid function tests on day 5 demonstrated a TSH 5.12mU/l, free T4 34.2pmol/l and free T3 8.5pmol/l, likely representing a euthyroid state at this age and the baby was asymptomatic. However, assessment a week later revealed tachycardia and significant abnormalities in TFTs with TSH suppressed at 0.07mU/l, free T4 >100pmol/l and free T3 18.3pmol/l in keeping with neonatal thyrotoxicosis. Neonatal treatment with carbimazole was commenced, titrated to thyroid function test results and stopped after 10 weeks with an excellent clinical and biochemical outcome.

Conclusion: This case highlights the importance of checking TSH receptor antibody titre during pregnancy in patients with a history of thyrotoxicosis and informing the paediatric team if the titre is raised. It also demonstrates that neonatal thyroid function testing shortly after birth can often be falsely reassuring due to the effect of trans-placental passage of maternal anti-thyroid drugs and that early reassessment of the infant and retesting of thyroid function at 7 days is essential.

Good communication between all clinical teams managing the patient is crucial.