What is the most appropriate investigation for a child with suspected atopic dermatitis who has not responded to topical corticosteroids and is suspected of having a food allergy?

Investigation for Suspected Food Allergy in Atopic Dermatitis Unresponsive to Topical Corticosteroids

The most appropriate investigation is limited food-specific IgE testing for common allergens (milk, eggs, wheat, soy, and peanuts), not broad panel testing, and only if the child is under 5 years old with moderate to severe disease that has truly failed optimized topical therapy. 1, 2

Critical First Step: Optimize Treatment Before Testing

Before pursuing any food allergy investigation, you must ensure the atopic dermatitis has been adequately treated, as this is a common pitfall. 1

• Verify that appropriate-potency topical corticosteroids were actually used - many cases labeled as "treatment failure" reflect inadequate therapy rather than food allergy. 1
• Ensure proper moisturizer use and skin care regimen - the foundation of AD management must be optimized first. 1
• Food allergy is only a contributing factor in approximately 35% of children with moderate to severe atopic dermatitis, so most cases will not have a food trigger. 1

When to Proceed with Testing

Limited food allergy testing is appropriate only when ALL of the following criteria are met: 1, 2

• Child is less than 5 years old 1
• Moderate to severe atopic dermatitis (not mild disease) 1
• Persistent disease despite truly optimized topical therapy and skin care 1, 2
• OR a reliable history of immediate allergic reaction (hives, respiratory symptoms, vomiting within 2 hours) after ingestion of a specific food 1

The Correct Investigation: Limited Specific IgE Testing

Test only for the five most common pediatric food allergens: cow's milk, eggs, wheat, soy, and peanuts. 1, 2

Why This Approach:

• Broad panel allergy testing without clinical history is explicitly not recommended - it leads to false-positive results that reflect sensitization rather than true allergy. 1
• Specific IgE testing has high negative predictive value (>95%) but low positive predictive value (40-60%), meaning negative results effectively rule out food allergy, but positive results require clinical correlation. 1
• Skin prick testing is an alternative, particularly useful if the child has extensive eczematous lesions, prominent dermatographism, or recent antihistamine use. 1

Why the Other Options Are Incorrect

Option A (IgE levels for common food allergies) - Partially Correct But Incomplete

• This is the right direction but must be limited testing only, not broad panels. 1, 2
• Testing must be preceded by proper optimization of topical therapy. 1, 2
• Measuring total serum IgE levels alone is not helpful - only food-specific IgE matters. 1

Option B (PPD skin test) - Completely Incorrect

• PPD (tuberculin skin test) has no role in evaluating food allergy or atopic dermatitis. [@General Medicine Knowledge@]
• This would be appropriate for tuberculosis screening, not this clinical scenario. [@General Medicine Knowledge@]

Option C (Continue food with supervision) - Dangerous Without Prior Testing

• Continuing suspected allergenic foods without evaluation risks missing IgE-mediated food allergy that could cause anaphylaxis. 1
• Supervised food challenges are the gold standard for diagnosis but should only be performed after initial testing and under controlled medical conditions with emergency equipment available. 1
• The double-blind, placebo-controlled food challenge (DBPCFC) is reserved for confirming diagnosis after positive screening tests. 1, 2

Critical Pitfalls to Avoid

Do not over-interpret positive test results. 1

• Positive specific IgE or skin prick tests only indicate sensitization, not necessarily clinical allergy. 1
• Confirmation requires either a positive oral food challenge or a convincing history of immediate reaction with positive testing. 1, 3

Do not implement elimination diets based solely on positive tests without clinical correlation. 1

• Unnecessary dietary restrictions can cause serious harm including growth delay, weight loss, calcium deficiency, and other nutritional deficiencies. 1, 2, 4
• Even when food allergy is confirmed, effective AD treatment still centers on good skin care and topical therapies. 1, 2

Do not refer for allergy testing if the child has not had optimized topical treatment first. 1, 2

• Many providers prematurely suggest food allergy as causative without adequately treating the underlying eczema. 1, 5

Next Steps After Testing

• If tests are negative: Food allergy is effectively ruled out; focus on optimizing AD management. 1
• If tests are positive: Refer to allergist for confirmation with supervised oral food challenge and long-term management. 1
• Children with confirmed food allergies often develop tolerance over time to milk, egg, soy, and wheat, requiring periodic re-testing. 1, 2