Differential Diagnosis for a 3-month-old Boy with Large-Volume Diarrhea and Failure to Thrive
- Single most likely diagnosis:
- Trypsin: The absence of enteropeptidase activity in the proximal intestinal villi is a key finding. Enteropeptidase is an enzyme that activates trypsinogen to trypsin, which is crucial for protein digestion. Impaired trypsin activity would lead to malabsorption of proteins, resulting in large-volume diarrhea and failure to thrive.
- Other Likely diagnoses:
- Lactase: Although the primary issue seems to be related to protein digestion, lactase deficiency could also contribute to diarrhea in an infant, especially if they are still on a lactose-containing diet.
- Bile salts: While the primary finding points towards an issue with protein digestion, bile salt deficiency could lead to fat malabsorption, contributing to diarrhea and failure to thrive.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Secretin: Although less directly related to the specific finding of absent enteropeptidase activity, secretin plays a crucial role in regulating pancreatic and bile duct secretions. A deficiency could lead to severe malabsorption.
- Rare diagnoses:
- Amylase: Amylase deficiency would primarily affect carbohydrate digestion. While it could contribute to gastrointestinal symptoms, it's less directly related to the specific findings in this case.
- Pepsin: Pepsin is involved in gastric protein digestion. While important, the findings suggest a issue further down the digestive tract, making this a less likely primary cause.