[Show abstract][Hide abstract] ABSTRACT: Patch testing is the standard clinical procedure to prove contact sensitization. It is a common practice to attach multiple patch tests at the same time. However, synchronous reactions to unrelated allergens may not be completely unassociated. If so, the reaction in a given test field might be influenced by other positive test reactions in a distance-related degree. This article analyses whether there is a distance-related effect of synchronous positive patch test reactions on the outcome of a target patch test.
Data collected from patients patch tested for diagnostic purposes with 15 standard allergens attached in a specific pattern between 1992 and 2004 in 20 centres in a Central European network were retrospectively evaluated. The association between the target patch test result (allergic vs negative reaction to the thiuram mix) and the number and cumulated strength of synchronous positive reactions (positive patch test load) to allergens placed in nearby or distant positions to the target patch was analysed by using logistic regression analysis.
The likelihood of a positive reaction to thiuram mix significantly increased with an increasing synchronous positive patch test load generated by positive reactions to allergens unrelated to thiuram mix. The effect of allergens neighbouring the target allergen was not significantly stronger than that of allergens placed in distant positions.
For the interpretation of patch test results, the potentially enhancing effects of a synchronous positive patch test load should be considered. The local distribution of the patches on the back is, however, not critical.
[Show abstract][Hide abstract] ABSTRACT: Using previously generated data from multicenter studies European Environmental and Contact Dermatitis Research Group (EECDRG) and North American Contact Dermatitis Group (NACDG), we compare patch test positivity of random sample and eczema populations, attempting to ascertain how one might extrapolate frequency from an eczema group to a general population. We included population-based mathematical estimates for patch test reaction in the general population using the Multinational MONItoring of trends and determinants in Cardiovascular disease MONICA and Clinical Epidemiology and Drug-Utilization Research (CE-DUR) systems. Data analysis provides a ratio of eczema population:random sample population for each allergen and an overall ratio of all allergens 5:1 for actual data and 6:1 for population-based estimates (according to the MONICA and CE-DUR systems). If the positivity rate were the same in each population, the ratio would approximate 1. The individual allergen ratios ranged from formaldehyde at 11.6 to parabens at 1.0, with respect to the NACDG. Some differences may be explained by exposure (neomycin) being greater in patients than in random population. Materials of ubiquitous exposure - i.e. fragrance mix and nickel - had ratios closer to 1. Taken together, data obtained in eczema patients may be viewed as part of a complex biology and may eventually be of use in aiding validation of predictive dermatotoxilogic assays and in public health assessments.
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