What is the most appropriate investigation for a child with suspected atopic dermatitis who has not responded to emollients and low-dose corticosteroids, where food allergy is suspected?

Most Appropriate Investigation for Suspected Food Allergy in Treatment-Resistant Atopic Dermatitis

In a child with atopic dermatitis not responding to emollients and low-dose corticosteroids where food allergy is suspected, the most appropriate investigation is a diagnostic elimination diet for 4-6 weeks followed by an oral food challenge under allergist supervision. 1, 2

Initial Testing Approach

For children under 5 years with moderate-to-severe atopic dermatitis that persists despite optimized topical therapy, consider limited food allergy testing specifically for cow's milk, eggs, wheat, soy, and peanuts. 3, 2 These five foods account for over 90% of food allergies in children with atopic dermatitis. 4

Testing Options Include:

• Skin prick testing - has high negative predictive value (>95%) but poor positive predictive value (40-60%), meaning a negative test effectively rules out IgE-mediated allergy but a positive test only indicates sensitization, not true allergy 1, 2

• Food-specific IgE blood testing - useful alternative when widespread skin lesions prevent skin testing or when marked dermatographism is present 2

Critical Diagnostic Sequence

The American Academy of Dermatology emphasizes that positive allergy tests alone (skin prick or IgE) should never be used to diagnose food allergy or initiate elimination diets without clinical correlation. 1, 2 This is because 50-90% of presumed food allergies based on symptoms or positive tests are not true allergies. 1

The Proper Diagnostic Algorithm:

1. Perform limited testing (if indicated by history or severity) for the five common allergens listed above 3, 2

2. If testing is positive AND there is consistent correlation between food exposure and dermatitis flares, initiate a diagnostic elimination diet for 4-6 weeks with the suspected food items 3, 1, 2

3. If the child's atopic dermatitis remains stable or worsens during elimination, the food is unlikely a relevant trigger and no further testing is needed 3

4. If improvement occurs during the elimination diet, an oral food challenge under allergist guidance is essential to confirm the diagnosis, as improvement may be coincidental or reflect placebo effect 3, 1, 2

5. Double-blind placebo-controlled food challenge is the gold standard, though open-label challenges are acceptable in clinical practice 3, 1

Important Caveats and Pitfalls

Food allergies are relevant triggers in only a small subset of atopic dermatitis patients (usually those with moderate-to-severe disease), and the true frequency is probably low. 3 The American Academy of Dermatology warns that excessively restrictive diets can cause weight loss, poor growth, calcium deficiency, hypovitaminosis, and kwashiorkor. 3, 1, 2

Common Mistakes to Avoid:

• Never initiate elimination diets based solely on positive skin tests or IgE levels without documented clinical symptoms - this leads to unnecessary dietary restrictions in 84-93% of cases 3

• Do not perform extensive allergy testing without clear medical history - positive results may only reflect sensitization rather than true allergy 2

• Avoid prolonged elimination diets without confirmed clinical relevance - multiple dietary restrictions should only be undertaken with documented, clinically relevant food allergies 3

• Remember that even with confirmed food allergy, avoidance diets are unlikely to affect the overall course of atopic dermatitis - they primarily prevent IgE-mediated immediate reactions 3

When Testing is Most Appropriate

Testing should be considered when: 3

• The child has moderate-to-severe atopic dermatitis despite optimized topical therapy
• There is a reliable history of immediate reaction after ingesting a specific food
• The child is under 5 years old with persistent disease
• A food diary shows consistent correlation between specific foods and symptom flares

If a patient has positive allergy tests but no history of symptomatic food allergy, consultation with an allergist is warranted to distinguish true allergy from sensitization alone, with discussion of benefits and risks of formal food challenge. 3