Hypothyroidism in Children

Abstract

1. Debra Counts, MD* 2. Surendra K. Varma, MD† 1. *Associate Professor of Pediatrics; Chief, Division of Pediatric Endocrinology, Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Md 2. †Editorial Board After completing this article, readers should be able to: 1. Describe the causes of hypothyroidism in infants and children. 2. Discuss the clinical presentation of and diagnostic approach to hypothyroidism. 3. Differentiate nonthyroidal illness low triiodothyronine (T3) syndrome from hypothyroidism. 4. Identify thyroid-binding globulin deficiency as a euthyroid state. 5. Recognize the importance of treatment and implications of inadequate treatment of hypothyroidism in the neonate and young child. Thyroid hormone is essential to growth and neurologic development in childhood. The thyroid begins to take shape at 7 weeks’ gestation, and thyroid hormone (T4, thyroxine) is produced starting at 12 weeks’ gestation. Thyroid dysfunction in the neonate, infant, or child has a significant impact on development. The goal of treatment is to assure normal growth and avoid developmental delay. ### Definition Neonatal hypothyroidism results from decreased T4 production in a newborn. It is the most preventable cause of potential intellectual disability. T4 is critical to the myelinization of the central nervous system (CNS) during the first 3 years after birth. In the healthy term baby, serum thyroid-stimulating hormone (TSH) concentrations normally rise abruptly to 60 to 80 mU/L within 30 to 60 minutes after delivery. The serum TSH concentration then decreases rapidly to about 20 mU/L by 1 day of age and subsequently more slowly to 6 to 10 mU/L by 1 week of age. This surge in TSH stimulates T4 secretion, with serum T4 concentrations peaking at 24 to 36 hours of age at 10 to 22 mcg/dL (128.7 to 283.2 nmol/L). Serum T3 concentrations also rise simultaneously to about 250 ng/dL (3.9 nmol/L), due to increased conversion of T4 to T3 in peripheral tissues and thyroidal secretion. T4, free T4, and T3 concentrations gradually fall in the first 4 weeks after birth to total T4 concentrations of 7 to 16 mcg/dL (90.1 to 205.9 nmol/L), free …