Differential Diagnosis for a Five Week Old Baby with Sulphur Odor and Failure to Thrive After Drinking Cow's Milk

• Single Most Likely Diagnosis

  • Galactosemia: This condition is characterized by the inability to metabolize galactose, a sugar found in lactose (milk sugar). When galactose is not properly broken down, it can lead to the accumulation of toxic substances, including galactose-1-phosphate, which can cause symptoms such as failure to thrive, liver dysfunction, and the production of a sulphur-like odor due to the accumulation of methyl mercaptan and other volatile organic compounds in the breath and urine.

• Other Likely Diagnoses

  • Lactose Intolerance: Although less severe than galactosemia, lactose intolerance can cause gastrointestinal distress, leading to malabsorption and potentially a failure to thrive. However, the sulphur smell is less commonly associated with lactose intolerance compared to galactosemia.
  • Cow's Milk Protein Allergy (CMPA): This is an immune-mediated reaction to one of the proteins in cow's milk (casein or whey). Symptoms can include digestive issues, skin rashes, and failure to thrive, but the sulphur odor is not typically a primary symptom.

• Do Not Miss Diagnoses

  • Maple Syrup Urine Disease (MSUD): This is a metabolic disorder caused by a deficiency in the enzyme that breaks down certain amino acids. It leads to a buildup of these amino acids and their byproducts in the blood and urine, giving urine a distinctive sweet odor reminiscent of maple syrup. However, in some cases, the odor can be more sulphur-like. It's crucial to diagnose MSUD early, as it can lead to severe neurological damage if left untreated.
  • Tyrosinemia Type 1: A genetic disorder characterized by the inability to break down the amino acid tyrosine, leading to the accumulation of toxic compounds. Symptoms can include failure to thrive, liver and kidney dysfunction, and a cabbage-like or sulphur-like odor in the breath or urine due to the accumulation of metabolites.

• Rare Diagnoses

  • Isovaleric Acidemia: A rare genetic disorder involving the inability to properly break down a particular amino acid (leucine), leading to the accumulation of isovaleric acid. This condition can cause a sweaty foot or cheese-like odor, but in some cases, it might be perceived as sulphur-like. Symptoms include severe metabolic acidosis, failure to thrive, and potentially life-threatening complications if not treated.
  • Methionine Malabsorption Syndrome (Smith-Strang disease): An extremely rare condition where the body cannot properly absorb methionine, an essential amino acid. It leads to a strong, characteristic odor (often compared to boiled cabbage or sulphur) in the urine and sweat due to the accumulation of alpha-amino-gamma-methylthiobutyric acid and other metabolites.