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Updated: Dec 9 2021

Congenital Hypothyroidism (Cretinism)

  • Snapshot
    • A 6-week-old girl presents with lethargy, difficulty feeding, and hypotonia. Her parents report that she was healthy and did not have any apparent symptoms at birth. This is her first time seeing a doctor. On exam, she appears jaundiced and has a large tongue that is protruding.
  • Introduction
    • Clinical definition
      • thyroid hormone deficiency present at birth
      • cretinism refers to the state of developmental delay secondary to untreated congenital hypothyroidism
    • Genetics
      • defects in T4 or triiodothyronine (T3) synthesis
  • Epidemiology
    • Demographics
      • most common neonatal endocrine disorder
      • 2:1 female-to-male ratio
    • Risk factors
      • gestational age > 40 weeks
    • Pathogenesis
      • thyroid hormone is critical for normal brain growth and myelination
      • during the first trimester, the fetus is dependent on maternal thyroxine (T4) with gradual fetal thyroid secretion after
      • major etiologies include
        • most common in developed countries
          • agenesis of the thyroid
          • inborn errors of metabolism
        • most common in underdeveloped countries
          • iodine deficiency
      • maternal antithyroid antibodies that cross the placenta is a rare cause
  • Presentation
    • Symptoms
      • normal APGAR, asymptomatic at birth
      • presents at 6-12 weeks
        • poor feeding
        • failure to thrive
        • lethargy
        • constipation
    • Physical exam
      • low body temperature
      • large anterior fontanelle
      • jaundice
      • coarse facies with macroglossia
      • umbilical hernia
      • hypotonia
      • developmental delay
      • mottled, dry skin
  • Studies
    • Diagnostic testing
      • diagnostic approach
        • screening at 3 days old or within 7 days of birth
          • false positives 24-48 hours after birth
          • false negatives in critically ill neonates
        • labs
          • thyroid stimulating hormone (TSH) and thyroxine (T4)
            • best initial screening via heel prick
        • imaging
          • scintigraphy (technetium-99m or iodine-123)
            • best for evaluating thyroid function
          • ultrasound
            • gold standard for measuring thyroid anatomy
            • not sensitive for detecting small ectopic glands
          • treatment should not be delayed while awaiting imaging studies
  • Differential
    • Neonatal hypothyroxinemia
      • distinguishing factor
        • ↓ thyroid hormone but TSH is not elevated, occurs in premature or ill infants
    • Pediatric hypopituitarism
      • distinguishing factor
        • loss of other axes in addition to ↓ T4 including ↓ cortisol, ↓ sex steroids, ↓ growth hormone, and ↓ antidiuretic hormone
    • Diagnostic criteria
      • ↑ TSH and ↓ T4
      • imaging can help differentiate etiology
  • Treatment
    • Management approach
      • early diagnosis via neonatal screening allows for early intervention
      • routine clinical and laboratory monitoring
      • formal developmental and psychoneurological evaluations
    • First-line
      • levothyroxine replacement
  • Complications
    • Intellectual disability
    • Growth failure
  • Prevention
    • Prevention by newborn screening by law
    • Dietary iodine supplementation can prevent endemic cretinism but is not indicated for sporadic congenital hypothyroidism
  • Prognosis
    • Early diagnosis and treatment improves outcomes and patients can develop normally
    • The most common preventable cause of intellectual disability
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