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

Diagnostic Approach for Food Allergy in Treatment-Resistant Atopic Dermatitis

The most appropriate investigation is D - food elimination diet followed by supervised food challenge, as this represents the gold standard diagnostic approach recommended by the American Academy of Dermatology for confirming food allergy in children with atopic dermatitis. 1, 2

Why Food Elimination is the Correct Answer

The American Academy of Dermatology explicitly recommends a diagnostic elimination diet for 4-6 weeks with suspected food items, followed by oral food challenge under allergist guidance to confirm the diagnosis. 1, 2, 3 This stepwise approach is critical because:

• Improvement during elimination may be coincidental or reflect placebo effect, making the subsequent challenge essential for confirmation 1, 2
• This is the only method that can definitively establish whether a food is truly causing eczematous flares versus mere sensitization 2, 3
• The double-blind placebo-controlled food challenge is considered the gold standard, though open-label challenges are acceptable in clinical practice 2, 3

Why Other Options Are Inadequate

IgE Testing and Skin Prick Tests Have Poor Positive Predictive Value

Both serum-specific IgE levels (option A) and skin prick testing (option B) have poor positive predictive values of only 40-60% and merely indicate sensitization, not true food allergy. 1, 2, 3

• The negative predictive value is high (>95%), making these tests useful for ruling out allergy but not confirming it 1, 3
• The American Academy of Dermatology states that 50-90% of presumed food allergies based on symptoms or positive tests are not true allergies 2
• Positive test results only signify sensitization and require clinical correlation through elimination and challenge to establish actual allergic disease 1

Critical Pitfall: Testing Without Clinical Correlation

Broad panel allergy testing independent of history is explicitly not recommended and leads to unnecessary dietary restrictions. 1, 3 Research demonstrates that 84-93% of avoided foods based primarily on sensitization testing could actually be tolerated when formally challenged 1

The Proper Diagnostic Algorithm

Step 1: Limited Initial Testing (If Indicated)

For children <5 years with moderate-to-severe atopic dermatitis not responding to optimized topical therapy, consider limited testing for cow's milk, eggs, wheat, soy, and peanut 1, 3

• This testing helps prioritize which foods to eliminate first 1, 3
• Testing should never be performed without clinical history suggesting food involvement 3

Step 2: Diagnostic Elimination Diet

Eliminate suspected foods for 4-6 weeks while maintaining optimal topical therapy 1, 2, 3

• If atopic dermatitis remains stable or worsens, the food is unlikely a relevant trigger and further testing is unnecessary 1
• If improvement occurs, proceed to Step 3 1, 2

Step 3: Supervised Oral Food Challenge

An oral food challenge under allergist guidance is essential to confirm the diagnosis 1, 2, 3

• This distinguishes true food allergy from coincidental improvement or placebo effect 1, 2
• The challenge should be performed in a controlled setting with appropriate monitoring 1

Important Clinical Caveats

Food Allergy is Rare in Atopic Dermatitis

Food allergies are relevant triggers in only a small subset of atopic dermatitis patients (approximately 30-37% of those with moderate-to-severe disease), and true food-induced eczematous reactions are actually rare. 1, 4, 5

• The exact impact of food exposure on atopic dermatitis course remains unclear 1
• Most reactions are immediate IgE-mediated (urticaria, anaphylaxis) rather than delayed eczematous flares 1, 4

Dangers of Unnecessary Elimination

Excessively restrictive diets can cause serious harm including weight loss, poor growth, calcium deficiency, hypovitaminosis, and kwashiorkor. 1, 2, 3

• Multiple dietary restrictions should only be undertaken with documented, clinically relevant food allergies 1
• Nutritional consultation is recommended when widespread avoidance is necessary 1

Do Not Abandon Topical Therapy

Effective treatment of atopic dermatitis remains skin care and topical therapies, even in the presence of confirmed food allergy. 3 The focus on food allergy often detracts from proper anti-inflammatory management 4, 6