Atopy and Sensitization to Allergens Known to Cause Systemic Contact Dermatitis

Is Food-Triggered Atopic Dermatitis a Form of Systemic Contact Dermatitis?

Food allergy in atopic dermatitis is mediated by complex immune interactions between genetics, diet, environment, and the microbiome. When contact between inflamed skin and food antigens occurs, contact hypersensitivity can develop. Consequently, systemic contact dermatitis (SCD) can occur after ingestion of allergenic foods or food additives in the setting of a Th2 response with CLA-positive T cells, triggering dermatitis where skin resident memory lymphocytes reside. This phenomenon explains food-triggered dermatitis. Atopy patch tests (APTs) detect sensitization to food proteins responsible for SCD, which in turn can be confirmed by oral food challenge with delayed interpretation. We summarize the literature on using APTs to identify foods for oral challenge with dermatitis as an outcome. In dermatitis patients at risk for Th2 skewing based on a history of childhood-onset flexural dermatitis, shared decision-making should include a discussion of identifying and avoiding food and food additive triggers, as well as identifying and avoiding all contact allergens, prior to initiation of systemic therapy for dermatitis.

Atopy patch tests may identify patients at risk for systemic contact dermatitis

Background

A subset of patients with positive patch tests demonstrates systemic contact dermatitis (SCD) upon ingestion or inhalation of the allergen. Concern has been raised about the use of patch tests for protein allergens (APTs) to detect SCD in atopic dermatitis (AD) patients.

Methods

We present atopy patch test (APT) data for 97 people. We reviewed APTs and tests for antigen‐specific immunoglobulin E (IgE) to the same allergen in pediatric AD patients. We compared the frequency of APTs as a function of age in AD patients. To study the irritancy potential of APTs, we prospectively tested consenting non‐AD dermatitis patients undergoing evaluation for allergic contact dermatitis and healthy controls to an APT panel.

Results

APT demonstrated fewer positive results than serum‐specific IgE or skin prick tests to the same allergen. Positive APT to food was more common in children under 3 years, whereas positive APT to aeroallergens were more common in teens and adults. Only positive APTs to dust mite were significantly more common positive in subjects without AD.

Conclusion

Our aggregate findings suggest that most APTs, but not dust mite, behave like conventional patch tests to low‐potency allergens. They are more likely to be positive in patients with chronically inflamed skin and to identify allergens that cause SCD. The higher prevalence of APT positivity to foods in young children is consistent with food allergy as a trigger of AD (also known as SCD) being more common in children than adults. Positive APTs define patients who may have SCD; negative APTs may guide elimination diets.