Can a milk allergy present as diarrhea in infants and young children?

Can Milk Allergy Present as Diarrhea?

Yes, milk allergy commonly presents with diarrhea in infants and young children through multiple distinct non-IgE-mediated mechanisms, and recognizing these patterns is critical because they require different diagnostic approaches than typical IgE-mediated allergies.

Clinical Presentations of Milk Allergy with Diarrhea

Food Protein-Induced Enteropathy Syndrome

This is the most severe diarrheal presentation and should be your primary concern when evaluating chronic diarrhea with failure to thrive. 1

• Presents as chronic diarrhea with steatorrhea in up to 80% of cases, accompanied by weight loss and growth failure 1
• Occurs in young infants and mimics celiac disease but appears earlier in life 1
• Characterized by generalized malabsorption of fat, carbohydrates, and other nutrients due to intestinal mucosal changes 1
• May develop moderate anemia, hypoproteinemia, and vitamin K deficiency 1
• Diagnosis requires clinical symptoms, resolution with milk elimination, and recurrence following oral food challenge 1, 2
• Virtually all patients outgrow symptoms by 2-3 years of age 1, 2

Allergic Proctocolitis

This is the most common and benign presentation in otherwise healthy infants. 1

• Manifests as mucoid, blood-streaked stools in an otherwise healthy infant 1, 2
• Can also present with chronic emesis, diarrhea, and failure to thrive 1
• Typically resolves in the first 1-2 years of life 1
• Associated with cow's milk, soy milk, or even breast milk ingestion 1
• Symptoms resolve within 48-72 hours following elimination of dietary cow's milk protein 3

Food Protein-Induced Enterocolitis Syndrome (FPIES)

While vomiting dominates, diarrhea is a key feature in chronic presentations. 1, 4

• Young formula-fed infants present with chronic emesis, diarrhea, and failure to thrive 3
• Acute re-exposure after elimination causes profuse, repetitive vomiting 1-4 hours post-ingestion 4, 3
• Up to 20% of acute exposures may cause hypovolemic shock requiring IV hydration 3
• Children with one non-IgE-mediated food allergy are at increased risk for developing FPIES to other foods 4

Critical Diagnostic Distinctions

Milk Allergy vs. Lactose Intolerance

You must distinguish between immune-mediated milk allergy and non-immune lactose intolerance—this is a common clinical pitfall. 1, 2, 5

• Lactose intolerance causes bloating, flatulence, and diarrhea due to lactase enzyme deficiency without immune involvement 1, 2, 5
• Milk allergy is immune-mediated and presents with the syndromes described above 1, 2, 5
• Children with milk allergy may experience hives and impaired breathing after exposure, which never occurs with lactose intolerance 1

Testing Limitations in Non-IgE-Mediated Disease

Standard allergy tests will be negative in diarrheal presentations—do not rely on them for diagnosis. 1

• Skin prick tests (SPT) and specific IgE (sIgE) tests are typically negative in allergic proctocolitis, enteropathy syndrome, and FPIES 1, 2
• These are non-IgE-mediated disorders involving T-cell mediated immunity (Type IV hypersensitivity) 5
• Diagnosis relies on clinical history, symptom resolution with elimination, and recurrence following oral food challenge 1, 2

Diagnostic Algorithm

Step 1: Characterize the Diarrhea Pattern

• Acute bloody stools in healthy infant → Consider allergic proctocolitis 1, 2
• Chronic diarrhea with steatorrhea, weight loss, growth failure → Consider food protein-induced enteropathy 1, 2
• Chronic diarrhea with vomiting and failure to thrive → Consider FPIES 4, 3

Step 2: Implement Elimination Trial

• Eliminate cow's milk protein from diet (or maternal diet if breastfeeding) 1, 2
• Expect symptom resolution within 48-72 hours for proctocolitis 3
• May require several weeks for enteropathy syndrome 1

Step 3: Confirm Diagnosis

• For proctocolitis and enteropathy: Oral food challenge after elimination period confirms diagnosis by symptom recurrence 1, 2
• For FPIES: Challenge must be done under physician supervision with secure IV access due to risk of hypovolemic shock 3

Management Priorities

Immediate Treatment

• Strict elimination of cow's milk protein from diet 2
• Use extensively hydrolyzed whey or casein formulas as first-line substitutes 2
• Soy formula is NOT recommended, particularly in infants under 6 months, due to cross-reactivity risk 2
• Partially hydrolyzed formulas are insufficient for treatment 2

Monitoring for Complications

• Monitor for nutritional deficiencies: anemia, hypoproteinemia, vitamin K deficiency in enteropathy syndrome 1
• Mandatory nutritional consultation when implementing elimination diets, especially with multiple food avoidances 2
• Assess growth parameters regularly 2

Natural History and Re-challenge

• Most children develop tolerance by 2-3 years of age for non-IgE-mediated disease 1, 2
• Follow-up oral food challenges at 6-month intervals are recommended to determine when elimination diets can be terminated 1
• Some children with positive RAST/skin tests at onset may not tolerate milk throughout childhood (32.5% in one study) 6

Common Pitfalls to Avoid

• Do not order IgE testing for suspected non-IgE-mediated presentations—negative results do not rule out milk allergy causing diarrhea 1, 2
• Do not confuse sensitization with allergy—positive tests without clinical symptoms do not constitute food allergy 2, 5
• Do not use soy formula as a substitute in young infants with confirmed milk allergy 2
• Do not perform oral food challenges for FPIES without IV access due to shock risk 3
• Do not attribute all diarrhea to milk allergy—optimize management of other conditions (like atopic dermatitis) before extensive food elimination 2