Answer:USMLE step 2 Mcq 170:A 5 days old neonate on total breast feeding presented with explosive, watery frothy stools and abdominal distention




Correct Answer: C

Primary lactose intolerance is the inherited deficiency of the enzyme lactase which is responsible for the breakdown and absorption of lactose present in the milk. Incomplete breakdown of lactose due to absence of the enzyme lactase results in an osmotic diarrhea.The diarrhea is observed within few days of starting of breast feeds and is typically explosive, watery with frothy stools. Due to the presence of undigested lactose the stool is acidic in pH which is responsible for the excoriation in the anal area.This causes anal excoriation.

Celiac's disease is hypersensitivity to gluten and is observed with the start of weaning diet and not with breast feeding. The stool is typically large and bulky not watery and frothy. 

Pseudomembranous colitis is an incorrect answer because it is an antibiotic associated colitis. It is rarely seen in infants and without history of use of antibiotics the diagnosis of Pseudomembranous colitis cannot be made.

Whipple's disease is a malabsorption syndrome seen in 4-5 decade of life and never in neonates.

Necrotizing enterocolitis is the acute infection due to bacterial colonization of the small and large intestines. It is a very serious condition and the child is typically extremely sick with high grade fever and frank blood in stool


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