Inborn errors of metabolism

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Background

  • Suspect in any sick neonate
  • Newborn screening varies by state
  • May present as late as early adulthood
  • Clinical manifestations are due to accumulation of toxic metabolites
  • Must rule-out sepsis (more common in these patients)

Clinical Features

Exam and history:

Differential Diagnosis

Sick Neonate

THE MISFITS [1]

Evaluation

  • Physical Exam:
    • Organomegaly
    • Neuro exam - tone, reflexes
    • Skin rashes
    • Eye exam
  • Labs:
    • Glucose level
    • Ammonia
      • Should be <100 in normal neonate
    • Lactate and pyruvate (drawn at same time)
    • Chemistry, hepatic panel
      • Anion gap (if >20, suggests an organic acidemia)
      • May see hypoglycemia, metabolic acidosis
    • Urinalysis (for ketones) or beta hydroxybutyrate in serum (very helpful to obtain prior to giving dextrose in hypoglycemic patients, if possible)
    • CBC
      • multiple organic acidemias can cause cytopenias
    • VBG
    • CPK in older kids and adolescents
  • Additional studies:
    • Consider head CT

Management

Must stop catabolism and acculmulation of toxins/ammonia

  1. Keep NPO
    • Removes potential inciting metabolic substrates
  2. IVF
    • Normal saline 20 mL/kg boluses
    • Once rehydrated, switch to IVF with dextrose (D10) at 1-2x maintenance
    • Increases renal excretion of toxic metabolites
  3. Hyperammonemia
  4. Sodium bicarbonate if acidotic

Cerebral edema

  • Hyperammonemia is risk factor
    • Mannitol 0.5gm/kg IV/IO
    • Do not give steroids (worsens hyperammonemia)

If seizing

Subsequent Management

  • Consider L-carnitine in conjunction with specialist, as some diseases may respond (but has side effects)

See Also

References

  1. Brousseau T, Sharieff GQ. Newborn emergencies: the first 30 days of life. Pediatr Clin North Am. 2006 Feb;53(1):69-84, vi.