How to diagnose a food allergy in a patient with atopic dermatitis who is not improving with topical steroid and ointment treatment?

Diagnostic Approach to Food Allergy in Atopic Dermatitis

The best approach to diagnose food allergy in a patient with atopic dermatitis not responding to topical steroids is a diagnostic food elimination diet (Option D) followed by oral food challenge if improvement occurs. 1

Why Food Elimination Diet is the Answer

Elimination diets should not be initiated based on suspicious history alone, but when allergy is suspected as a trigger, a diagnostic elimination diet for 4-6 weeks with suspected food items is the recommended diagnostic approach. 1 This is superior to the other options for the following reasons:

Problems with Other Testing Methods

• Skin prick testing (Option A) and food-specific IgE (Option C) have poor positive predictive value (40-60%) and only indicate sensitization, not true food allergy 1
• These tests have excellent negative predictive value (>95%) to rule out allergy, but positive results require clinical correlation and confirmation 1
• 50-90% of presumed food allergies based on symptoms or positive tests are not true allergies 1
• Measuring total serum IgE alone is not helpful in determining food allergy 1

The Diagnostic Algorithm

Step 1: Clinical History and Food Diary

• Use a food diary recording symptoms and intake to identify specific foods 1
• Look for consistent correlation between food exposure and dermatitis flares 1

Step 2: Diagnostic Elimination Diet (4-6 weeks)

• If consistent correlation exists, eliminate the suspected food for 4-6 weeks 1
• In children <5 years with moderate-to-severe AD not responding to optimized therapy, consider testing cow's milk, eggs, wheat, soy, and peanut 1
• For older patients, consider tree nuts, shellfish, fish, and pollen-related foods (apples, celery, carrots, hazelnuts in birch pollen allergy) 1

Step 3: Interpret Results

• If AD remains stable or worsens during elimination: the food is unlikely a relevant trigger 1
• If AD improves during elimination: proceed to oral food challenge 1

Step 4: Oral Food Challenge (Gold Standard)

• An oral food challenge under allergist guidance is essential to confirm the diagnosis, as improvement may be coincidental or placebo effect 1
• Double-blind placebo-controlled food challenge is the gold standard, though open-label challenges are acceptable in clinical practice 1
• Must be performed with trained personnel and emergency equipment available 1

Critical Pitfalls to Avoid

Unnecessary Dietary Restrictions

• Food allergies are relevant triggers in only a small subset of AD patients (usually moderate-to-severe disease) 1
• Excessively restrictive diets can cause weight loss, poor growth, calcium deficiency, hypovitaminosis, and kwashiorkor 1
• Studies show 84-93% of avoided foods based on sensitization alone could be safely returned to the diet 1

Over-reliance on Testing

• Never base elimination diets on positive skin tests or IgE alone without clinical correlation 1
• Positive tests only indicate sensitization; clinical relevance must be established 1

Proper Medical Supervision

• Multiple dietary restrictions require nutritional counseling from a dietician and supplementation 1
• Even with confirmed food allergy, avoidance diets are unlikely to affect the overall course of AD 1
• Effective AD treatment still centers on good skin care and topical therapies regardless of food allergy status 1

Important Context

It is extremely rare to find one allergen responsible for AD, which is a complex multifactorial disease involving non-allergic factors like climate and secondary infection. 1 The true frequency of food allergies causing isolated AD flares is probably low, and there is frequent misattribution of AD flares to food-related issues. 1