Abstract
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.