Metabolic Causes of CVS in a 10-Year-Old Girl
In a 10-year-old girl with cyclic vomiting syndrome, you must actively screen for metabolic disorders—particularly fatty acid oxidation defects and mitochondrial disorders—as these are treatable causes that can be fatal if missed.
Key Metabolic Disorders to Consider
The most important metabolic causes to rule out in pediatric CVS include:
Fatty Acid Oxidation (FAO) Disorders
- Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency - the most common FAO disorder that can masquerade as CVS 1
- Multiple acyl-CoA dehydrogenase deficiency (MADD/Glutaric Aciduria Type II) - can present with episodic vomiting triggered by high-fat foods, as demonstrated in a recent case of a 10-year-old girl initially misdiagnosed with CVS 2
- Short-chain 3-hydroxy acyl-CoA dehydrogenase (SCHAD) deficiency - presents with clinical features closely resembling CVS 3
- Late-onset glutaric acidemia type II - frequently misdiagnosed as CVS 3
Mitochondrial Disorders
Mitochondrial dysfunction may play a role in true CVS, but primary mitochondrial disorders can present with an identical cyclic vomiting phenotype 1. These warrant consideration, though they represent only 0.4% of cases in systematic reviews 4.
Other Metabolic Causes
- Urea cycle defects 1
- Organic acidurias 1
- Acute intermittent porphyria (though rare in this age group) 1
Critical Clinical Red Flags
You must urgently investigate for metabolic disease if any of these features are present:
- Non-ketotic hypoglycemia with metabolic acidosis - this is a cardinal feature of FAO disorders and demands immediate metabolic specialist referral 5
- Episodes triggered by fasting, illness, or high-fat meals 2
- Raised anion gap metabolic acidosis during episodes 5
- Persistent severe CVS requiring frequent hospitalizations 5
- Developmental delay or regression
- Family history of sudden infant death or unexplained childhood deaths
Diagnostic Approach
First-Line Screening (During or Immediately After an Episode)
Obtain these tests during an acute episode when possible, as metabolic abnormalities may normalize between episodes 6:
- Serum glucose (check for hypoglycemia)
- Venous blood gas (assess for metabolic acidosis and anion gap)
- Serum ammonia (elevated in urea cycle defects)
- Serum lactate (elevated in mitochondrial disorders)
- Urine ketones (absent ketones with hypoglycemia suggests FAO disorder)
Second-Line Definitive Testing
If screening is abnormal or clinical suspicion remains high 6:
- Urine organic acids - essential for detecting organic acidurias and FAO disorders 2
- Plasma acylcarnitine profile - detects FAO disorders and organic acidurias
- Plasma amino acids - screens for urea cycle defects
- Genetic testing - targeted gene panels (ETFDH, ACADM, HADHA genes) 2
Important Caveat
Testing between episodes may be falsely normal 6. If initial screening during a well period is negative but clinical suspicion persists, repeat testing during the next acute episode is mandatory.
Management Pending Results
Critical: Treat as if metabolic disease is present until definitively ruled out 6. This prevents potentially fatal complications:
- Avoid fasting - provide frequent carbohydrate-rich meals
- During episodes: IV dextrose (10% dextrose at 1.5× maintenance rate)
- Avoid high-fat meals
- Consider empiric L-carnitine supplementation (safe even if not deficient)
- Ensure adequate hydration
Prevalence Context
While metabolic diseases are uncommon causes of CVS (collectively <5% of cases 4), they are the treatable, life-threatening diagnoses you cannot afford to miss. The case fatality of undiagnosed MADD presenting as "CVS" has been documented 5, and a recent 2024 case report specifically describes a 10-year-old girl with glutaric aciduria type II initially misdiagnosed as CVS 2.
Common Pitfall to Avoid
The most dangerous error is accepting CVS as a diagnosis of exclusion without adequate metabolic screening 1. CVS remains underdiagnosed, but so do metabolic disorders presenting with cyclic vomiting. The presence of typical CVS features (prodromal symptoms, stereotypical episodes, migraine family history) does not exclude metabolic disease—these can coexist or the metabolic disorder can mimic CVS perfectly 5, 3.