The role of allergy in atopic dermatitis is unclear. IgE-mediated hypersensitivity may play a part in the pathogenesis of atopic dermatitis, with 50 percent of patients eventually having asthma and 80 percent having asthma or allergic rhinitis. Also, about two thirds of patients have a family history of atopy. Increased IgE concentrations can be found in 80 percent of these children, with most having positive immediate skin test reactions to various dietary and environmental allergens. The identification of food hypersensitivity and elimination of the offending foods from the diet significantly improve atopic dermatitis. Burks and associates examined the prevalence of food hypersensitivity in patients with atopic dermatitis and assessed the use of skin-prick tests with a limited number of food allergens.
A total of 165 patients from four months to 21.9 years of age with mild to severe dermatitis underwent allergy skin-prick tests with a battery of at least 12 food antigens, plus other foods that parents thought were causing symptoms. Parents were then asked to eliminate specific foods from the diet based on the results of the skin-prick test. After two to three weeks, a double-blind, placebo-controlled food challenge was performed with random sequences of placebo and food content. All reactions were recorded.
Ninety-eight patients (60 percent) had at least one positive food skin-prick test. When challenged with the offending food, positive symptoms demonstrated a 100 percent sensitivity, 66 percent specificity, 65 percent positive predictive value and 100 percent negative predictive value for skin testing. The onset of symptoms occurred within two hours of ingesting the food antigen in all cases and consisted mainly of skin symptoms. Other symptoms included gastrointestinal distress and respiratory symptoms. Seven foods (milk, egg, peanut, soy, wheat, cod/catfish and cashew) accounted for 89 percent of the positive challenges. Evaluating the utility of limited skin-prick testing for these seven foods resulted in a positive test having 97 percent sensitivity, 61 percent specificity, 61 percent positive predictive value and 97 percent negative predictive value.
The authors conclude that a large number of patients with atopic dermatitis have positive food challenges. This appears to be exacerbated by IgE-mediated mechanisms. Food elimination diets based solely on history have proved to be inadequate. Children with atopic dermatitis that is unresponsive to routine therapy should be evaluated for food hypersensitivity with a food challenge guided by skin-prick tests. Screening for food hypersensitivity should include milk, egg, peanut, wheat, soy, fish and tree nuts. Since sensitivity decreases or ends in a significant number of children, repeat challenges are a necessary part of ongoing care.