A 3-day-old neonate is identified on newborn screening with TSH >50 mU/L and low free T4. She appears well with mild hypotonia. The etiological classification of neonatal hypothyroidism and the MOST common cause is:
- A Central (secondary) hypothyroidism from pituitary TSH deficiency
- B Transient hypothyroidism from maternal antithyroid drugs
- C Thyroid dysgenesis (ectopia, aplasia) — most common cause accounting for 80-85% ✓
- D Dyshormonogenesis due to thyroid peroxidase gene mutation
Explanation
Congenital hypothyroidism occurs in 1:2000-4000 live births. Thyroid dysgenesis — comprising thyroid ectopia (most common; 60-70%), thyroid aplasia, and hypoplasia — accounts for approximately 80-85% of permanent congenital hypothyroidism. The remainder is due to dyshormonogenesis (inborn errors of thyroid hormone synthesis; 10-15%), maternal factors (transient), and central hypothyroidism (rare). Newborn screening (elevated TSH) detects primary hypothyroidism. Prompt levothyroxine treatment within the first 2 weeks of life is critical to prevent intellectual disability. Central hypothyroidism has low or normal TSH with low T4.
Reference: Ghai Essential Pediatrics, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.