Neonatal hyperthyroidism in an extremely low birth weight infant born to a mother with Graves' disease

Neonatal hyperthyroidism (NH) mostly commonly occurs in infants born to mothers with Graves' disease. NH in extremely low birth weight (ELBW) infants has been rarely described. Here, we report a case of NH in an infant born at 29 wk 6 d of gestation with a birth weight of 825 g. The mother had untreated Graves' disease during pregnancy. During the 2^nd wk of life, the infant developed persistent tachycardia (heart rate > 160 beats per min). Diagnosis of NH was made according to the results of her thyroid function: thyroid-stimulating hormone,< 0.005 mU/L (Reference range: 0.8-12.0 mU/L); free triiodothyronine, 5.1 pg/mL (Reference range: 2.3-4.2 pg/mL); free thyroxine, 38.5 pmol/L (Reference range: 10-33 pmol/L); and thyroid-stimulating hormone receptor antibody, 7.6 IU/L (Reference range: ≤ 1.22 IU/L). Carbimazole was administered. After 1 wk of treatment, levothyroxine was added due to a rapid decline in thyroid function. The treatment regimen was adjusted to achieve normal thyroid function. Her heart rate normalized with no significant hemodynamic instability or long-term complications during her hospitalization or follow-up visits. NH should be considered in ELBW infants with a maternal history of Graves' disease who present with persistent tachycardia. Monitoring thyroid function may be required more closely in ELBW infants when NH management is administered.