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

Most Appropriate Investigation for Suspected Food Allergy in Atopic Dermatitis

The most appropriate investigation is D - Food elimination diet followed by supervised food challenge, as this represents the diagnostic gold standard and stepwise approach recommended by major dermatology and allergy guidelines. 1, 2

Why Food Elimination Followed by Challenge is the Answer

The American Academy of Dermatology explicitly recommends against starting elimination diets or performing extensive testing without a clear stepwise approach: initial limited testing (if indicated), followed by a 4-6 week diagnostic elimination diet, and then supervised oral food challenge to confirm the diagnosis. 1, 2

The Diagnostic Algorithm

1. First, optimize topical therapy - Many children have inadequately treated atopic dermatitis, not food allergy. Ensure appropriate-potency topical corticosteroids and adequate emollient use before attributing symptoms to food allergy. 3, 1

2. Consider limited testing only in specific circumstances - In children under 5 years with moderate-to-severe atopic dermatitis that persists despite optimized topical treatment, consider testing for milk, eggs, wheat, soy, and peanuts. 3, 1, 2

3. Perform diagnostic elimination diet - If there is consistent correlation between food exposure and dermatitis flares, eliminate suspected foods for 4-6 weeks. 1, 2

4. Confirm with supervised oral food challenge - This is essential because improvement during elimination may be coincidental or placebo effect. The double-blind, placebo-controlled food challenge is the gold standard, though open-label challenges are acceptable in clinical practice. 1, 2, 4

Why the Other Options Are Incorrect

Option A (IgE levels) and Option B (Prick skin test) Are Inadequate Alone

• Skin prick testing and food-specific IgE have poor positive predictive value (40-60%) and only indicate sensitization, not true food allergy. 2
• The American Academy of Dermatology warns that 50-90% of presumed food allergies based on symptoms or positive tests are not true allergies. 2
• Allergy testing is not accurate enough to predict what someone may be allergic to and can only help in the evaluation of a suspected allergic reaction that has occurred. 3
• These tests have high negative predictive value (>95%) but cannot confirm clinical food allergy without challenge testing. 1, 5

Critical Pitfall to Avoid

Often, avoidance is prescribed based solely on positive testing and no treatment for the underlying atopic dermatitis is provided, which is incorrect management. 1 The evidence shows that food-induced eczematous reactions are actually rare - in one controlled study, only 1 positive eczematous food response was observed out of 58 challenges in children with severe atopic dermatitis. 5

Important Clinical Context

• Food allergy is a potential cause in only 35% of children with moderate-to-severe atopic dermatitis, not the majority. 3
• Up to 37% of children younger than 5 years with moderate-to-severe atopic dermatitis have IgE-mediated food allergy. 3
• Prolonged and multiple elimination diets can be harmful, leading to weight loss, growth delay, calcium deficiency, and other nutritional deficiencies. 1, 2
• Effective treatment of atopic dermatitis remains skin care and topical therapies, even in the presence of confirmed food allergy. 1

When to Refer to an Allergist

Referral to an allergist is recommended for longitudinal care, diagnostic testing, formulation of emergency anaphylaxis action plan, and supervised oral food challenges. 1 The allergist will help facilitate proper elimination diets under specialist supervision and prevent unnecessary dietary restrictions. 1