Atopy patch test in the diagnosis of food allergy in children with atopic eczema dermatitis syndrome 

Cudowska B*, Kaczmarski M

Abstract

Puropose: Food allergy has been demonstrated to play an important role in the pathogenesis of atopic eczema dermatitis syndrome (AEDS), affecting often atopic infants and young children. The most commonly offending foods are cow’s milk, hen’s egg, wheat and soy; implicating immediate (IgE-mediated) and late-phase (T-cells) immunological reactions in the pathogenesis of skin lesions. The diagnostic work-up of suspected immediate food reactions includes skin prick tests (SPT) and the measurement of food-specific antibodies (sIgE). The methodology of atopy patch test (APT) has been reported as a diagnostic tool with high predictive capacity for late-phase clinical reactions in children with atopic dermatitis. Although APT has been introduced into the diagnostic procedure for food allergy, its diagnostic accuracy remains still controversial; especially in older children. The aim of study was to evaluate the diagnostic accuracy of the atopy patch test in the detection of food allergy in correlation with SPT, sIgE and positive oral food challenge to milk, in children suffering from AEDS and to assess the sensitivity and specificity of this method in dependence on the age of investigated children. 
Material and methods: 34 children (25 boys, 9 girls) aged 5 months-16 years with suspicion of milk-related AEDS were investigated. These patients were subdivided into 2 age groups: group A – 20 children (<3 years), group B – 14 children (>3 years). The diagnostic procedures as skin-prick tests and atopy patch test were performed. The specific IgE to cow’s milk allergens were also measured. The open and blind diagnostic oral food challenge were performed to verify the results of tests. Sensitivity, specificity, positive (PPV) and negative (NPV) predictive value of APT were calculated in both age groups. 
Results: A positive challenge response to milk was found in 65.0% of investigated children in group A and in 35.7% in group B. No statistical differences in the prevalence of immediate (p<0.1905) and delayed-type (p<0.409) reactions has been found between age groups. Positive APT to milk were noticed in 55.0% of patients in group A and in 35.7% of children from group B, that has been in correlation with positive delayed-type reactions in oral food challenge in 72.7% and 80.0% in corresponding age groups. Polysensitization to other food allergens confirmed by SPT and/or sIgE was detected in 35.0% of patients younger than 3 years of age and in 50.0% of older children. The prevalence of positive APT to other foods (soy, rice, maize, cereals) was significantly higher (p<0.0073) in the polysensitized children from group A. Sensitivity of SPT/sIgE in children with immediate-type reactions to milk was 100%, specificity 94%. Sensitivity of APT to cow’s milk in children with late-phase reactions was 80% in both age groups; specificity 70%/89% with comparable PPV in both groups (73%/80%). Parallel skin testing with combined patch test and evaluation of sIgE enhanced the value of sensitivity to 92% in the group A and specificity to 89% in the group B. For PPV corresponding figures were 85%/80%.
Conclusions: APT was found to be more sensitive and specific method than SPT/sIgE in diagnosing delayed food allergy in children with AEDS. No age correlation between positive results of APT and oral food challenge and higher specificity of APT in older children confirm its accuracy in diagnosing delayed cow’s milk allergy in all age groups of children. Combined skin prick and patch testing significantly enhances identification of food allergy in children with AEDS. The outcome of the APT with food does not seem to be influenced by age of children, but because of its variability of sensitivity and specificity, a diagnosis of food allergy should be confirmed by oral food challenge.

Key words: 	atopic eczema dermatitis syndrome, food allergy, atopy patch test, skin-prick tests, specific IgE, oral food challenge.

Abbreviations: 	AEDS – atopic eczema dermatitis syndrome; APT – atopy patch test; CI – confidence interval; DBPCFC – double blind placebo controlled food challenge; IgE – immunoglobulin E; LR – likelihood ratio; NPV – negative predictive value; PPV – positive predictive value; sIgE – specific IgE; SPT – skin-prick tests.