Paediatrics: Inborn error of metabolism

2021-03-09 12:00 AM

Inborn errors of metabolism are rare. If such conditions are suspected during the neonatal period, then there is a specific course of action that should be followed.

Inborn error of metabolism

Inborn errors of metabolism are rare. If such conditions are suspected during the neonatal period, then there is a specific course of action that should be followed. Very occasionally, however, infants or children present outside the neonatal period with a catabolic state induced by an intercurrent illness such as viral infection, or fasting. The differential diagnosis at this time is broad and includes:

  • Infection: generalized sepsis; CNS infection.
  • Gastrointestinal: pyloric stenosis; gastroenteritis.
  • Cardiac: duct-dependent CHD.

Clinical assessment

History

  • A thorough history is important.
  • Assess whether there is any consanguinity or death of siblings from unknown or metabolic diseases.
  • Identify specifically developmental progress.
  • Has there been intermittent vomiting, sleepiness, or seizures?

Examination

  • A full examination is needed here.
  • Think about abnormal odours.
  • Check on growth, failure to thrive.
  • Skin: dermatitis or alopecia.
  • Eyes: cataracts.
  • Breathing pattern: Kussmaul or central hyperventilation.

Investigations

Until you know the diagnosis, the key tests are as follows.

Blood

  • FBC with differential.
  • Serum electrolytes with urea and creatinine. 
  • Glucose, LFTs (transaminases).
  • Arterial or capillary blood gas.
  • Lactate, pyruvate, ketones.
  • Plasma amino acids.
  • Ammonia.
  • Carnitine.
  • Drug screen.

Urine

  • Urinalysis.
  • Ketones. 
  • Reducing substances.
  • Organic acids.
  • Amino acids.
  • Drug screen.

Monitoring

Ensure the ABCs. Then, the form and type of monitoring will be dictated by the patient’s condition. Start with continuous pulse oximetry and ECG monitoring, and intermittent BP monitoring. Follow hourly output.

Therapy

In the acute setting, prior to transfer (if needed), treatment will be supportive and directed towards any complicating metabolic acidosis or hypoglycaemia. All protein intake and oral feeds should be discontinued until the diagnosis is confirmed. In order to avoid catabolism give continuous glucose infusion (10–15%) during illness or periods of fasting.

Supportive care

  • The underlying or precipitating illness needs to be treated.
  • Later on, as a means of prevention against infection, ensure that immunizations are up to date.

Acidosis

  • Correct and optimize ventilation and circulation.
  • After this, bicarbonate replacement may be needed.
  • For more persistent problems, treat in specialist centres.

Hypoglycaemia

Use glucose 25% (2–4mL/kg/dose IV).