Clinical Scenario:
A 10-day-old male infant is brought to the emergency department with poor feeding, vomiting, lethargy, and abnormal movements. He was born at term after an uneventful pregnancy. Examination shows hypotonia with intermittent dystonia. Laboratory investigations reveal metabolic acidosis, elevated plasma leucine, isoleucine, and valine levels, and urine organic acid analysis shows increased branched-chain ketoacids. The urine has a characteristic sweet odor. Which of the following is the most appropriate initial management?
A) High-protein diet supplementation
B) IV glucose with branched-chain amino acid restriction
C) Oral iron supplementation
D) Sodium bicarbonate alone
E) Insulin infusion
Correct answer & Explanation:
Correct Answer:
B) IV glucose with branched-chain amino acid restriction
Explanation:
This infant has Maple Syrup Urine Disease (MSUD), caused by deficiency of the branched-chain α-ketoacid dehydrogenase complex, resulting in accumulation of branched-chain amino acids (leucine, isoleucine, and valine) and their corresponding ketoacids.
Typical features include:
- Onset in the neonatal period
- Poor feeding and vomiting
- Lethargy and encephalopathy
- Hypotonia followed by abnormal movements/dystonia
- Metabolic acidosis
- Elevated branched-chain amino acids
- Sweet-smelling urine (“maple syrup” odor)
Why Option B is correct:
During an acute MSUD crisis, the goals are:
- Stop catabolism → IV glucose (with adequate calories) to suppress endogenous protein breakdown.
- Reduce toxic amino acid accumulation → restrict branched-chain amino acids.
- Consider specialized amino acid mixtures and dialysis if leucine levels remain dangerously high.
Why other options are incorrect:
A) High-protein diet supplementation
- Increases leucine, isoleucine, and valine levels and worsens neurological toxicity.
C) Oral iron supplementation
- Has no role in MSUD management.
D) Sodium bicarbonate alone
- May correct acidosis temporarily but does not remove toxic branched-chain amino acids.
E) Insulin infusion
- Does not treat the metabolic defect and may cause hypoglycemia.
