What could be causing a patient's bloody stools, watery/mucousy diarrhea, and increased bowel movements after introducing peanuts into their diet?

Differential Diagnosis and Management of Bloody Diarrhea in an Infant After Peanut Introduction

This presentation of bloody, mucousy diarrhea with increased bowel movements following recent peanut introduction most likely represents either food protein-induced allergic proctocolitis (FPIAP) or infectious gastroenteritis, and requires clinical evaluation with stool studies to differentiate these conditions. 1

Clinical Assessment Priority

The presence of blood and mucus in stool constitutes an alarm feature that mandates investigation for organic disease rather than functional disorders. 2 While the patient is currently behaving, eating, and sleeping normally, the combination of:

• Increased bowel movements (5 versus baseline 0-2 per day)
• Watery/mucousy consistency
• Visible blood in stool (not just on wiping)
• Recent introduction of a new allergenic food (peanut)

requires systematic evaluation. 1

Most Likely Diagnoses

Food Protein-Induced Allergic Proctocolitis (FPIAP)

The temporal relationship between peanut introduction "a few days ago" and onset of bloody, mucousy stools strongly suggests FPIAP as the primary consideration. 1 This non-IgE mediated food allergy typically presents with:

• Blood-streaked, mucousy stools
• Otherwise well-appearing infant
• Onset within days to weeks of allergen introduction
• Most commonly triggered by cow's milk and soy, but can occur with peanut 1

The fact that the infant is "behaving fine, eating fine, sleeping normally" is consistent with FPIAP, where systemic symptoms are typically absent. 1

Infectious Gastroenteritis

Infectious diarrhea must be ruled out, particularly given the acute onset. 1 Key considerations include:

• Bacterial pathogens (Salmonella, Shigella, Campylobacter) can present with bloody, mucousy diarrhea and fever 1
• Viral gastroenteritis typically causes watery diarrhea without blood
• The absence of fever and normal behavior makes severe bacterial infection less likely but does not exclude it 1

Immediate Recommended Actions

1. Stool Studies (Priority)

Obtain comprehensive stool evaluation before any treatment decisions: 1

• Bacterial culture for Salmonella, Shigella, Campylobacter
• Stool for ova and parasites
• C. difficile testing (though unlikely without antibiotic exposure)
• Fecal leukocytes or lactoferrin to assess for inflammatory process 2
• Fecal calprotectin if available - highly sensitive for intestinal inflammation and can help differentiate allergic from infectious causes 2

2. Assess Hydration Status

Evaluate for signs of dehydration: 1

• Thirst level
• Urine output frequency
• Skin turgor
• Mucous membrane moisture
• Behavioral changes (lethargy)

Oral rehydration should be initiated if any signs of volume depletion are present. 1

3. Dietary Management Pending Workup

Immediately eliminate peanut from the diet given the temporal relationship and high suspicion for FPIAP. 1

If breastfed, maternal elimination of peanut should be considered if FPIAP is confirmed. 1

When to Escalate Care

The patient should be seen urgently (same day or next day) if: 1

• Fever develops
• Increased blood in stool
• Signs of dehydration emerge
• Behavioral changes (lethargy, irritability)
• Decreased oral intake
• Worsening abdominal pain or distension
• Increased stool frequency beyond current level

The patient requires immediate emergency evaluation if: 1

• Hemodynamic instability
• Severe abdominal pain
• Altered mental status
• Signs of severe dehydration

Common Pitfalls to Avoid

Do not assume this is simple diaper irritation despite the relative's suggestion - true blood in stool (not just perianal irritation) requires investigation. 1, 2

Do not delay stool studies - infectious causes need prompt identification, and some pathogens require specific antimicrobial therapy. 1

Avoid antimotility agents - these are contraindicated in bloody diarrhea due to risk of complications. 1

Do not continue peanut exposure pending evaluation - if this is FPIAP, continued exposure will perpetuate symptoms and mucosal injury. 1

Follow-Up Based on Results

If Stool Studies Are Negative for Infection:

• Diagnosis of FPIAP becomes most likely
• Continue peanut elimination
• Monitor for symptom resolution (typically 72-96 hours)
• Consider allergy/gastroenterology referral for guidance on future peanut reintroduction 1

If Infectious Pathogen Identified:

• Treat according to specific pathogen and clinical severity 1
• Most bacterial gastroenteritis in well-appearing infants is self-limited
• Antimicrobial therapy indicated for Shigella and severe cases of Salmonella or Campylobacter 1

The key is obtaining the photograph as requested and ensuring timely clinical evaluation with appropriate stool studies to guide definitive management. 1