A 3-week-old neonate is noted to have prolonged jaundice, constipation, large tongue, umbilical hernia, and poor feeding. TSH from newborn screening is 285 mIU/L (normal <20). Free T4 is undetectable. The most common etiology and the critical parameter for determining outcome is:

• A Transient hypothyroidism from maternal antithyroid drugs — resolves without treatment
• B Dyshormonogenesis (inborn error of thyroid hormone synthesis) — requires iodine supplementation
• C Central hypothyroidism — TSH would be inappropriately low or normal
• D Thyroid dysgenesis (ectopic or absent thyroid) — most common cause of congenital hypothyroidism; adequacy and early initiation of levothyroxine replacement determines IQ outcome ✓

Explanation

Thyroid dysgenesis (ectopic thyroid, aplasia, or hypoplasia) accounts for 80–85% of permanent congenital hypothyroidism. The most critical factor for normal neurocognitive outcome is early initiation (ideally within 2 weeks of birth) of adequate levothyroxine (10–15 mcg/kg/day). Delayed or inadequate treatment results in irreversible intellectual disability (cretinism). Neonatal screening programs exist specifically for this preventable cause of intellectual disability. TSH would be inappropriately normal/low in central hypothyroidism.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.