The validity of rating patch test reactions based on digital images

BACKGROUND: The proper reading of patch test (PT) reactions, based on morphological criteria, is of utmost importance. Digital images are increasingly used for medical training. OBJECTIVES: To assess the diagnostic validity of readings of 20 digital images of various PT reaction grades by congress attendants. METHODS: 122 volunteers took a PT quiz offered during the 8th ESCD meeting, September 2006, Berlin. No information on the respective allergen was given, nor the gold standard grading determined by an European Environmental and Contact Dermatitis Research Group (EECDRG) expert panel was disclosed while the quiz was open. RESULTS: Overall, 63.5% of all ratings agreed 'exactly' with the gold standard, and 87.8% 'grossly', that is, with regard to the distinction between non-positive [doubtful or irritant (IR)] and positive (+, ++, and +++) reactions. Most images prompted a fair proportion of correct classifications. The distinction between doubtful and + and between +++, and strong bullous IR reactions proved partly difficult, probably because of blinding of the test substance. The least experienced in particular tended to misclassify IR reactions. CONCLUSIONS: The rating of digital images of PT reactions represents just 1 particular, isolated aspect of PT evaluation. Results were largely valid. Thus, the method could be used for continuing medical education, and for standardization in multicentre networks.