CD25 Seeing beyond ICDRG: dermoscopic signatures and reclassification of patch test reactions

Abstract

Dermatitis to para-phenylenediamine (PPD) and parthenium is a major cause of allergic contact dermatitis (ACD). Patch testing remains the gold standard for diagnosis, while conventional International Contact Dermatitis Research Group (ICDRG) grading is based on clinical morphology. Dermoscopy has emerging utility in inflammatory dermatoses including ACD. The aim of this study was to characterize dermoscopic features of parthenium and PPD patch test reactions across ICDRG grades and to reclassify clinical reactions. This was a case series on parthenium-positive (n = 20) and PPD-positive (n = 26) patch test reactions in the Indian standard series. Predefined dermoscopic parameters were assessed, including extent of erythema; erythema morphology; globular, vascular and follicular changes; and pigmentation. Dermoscopic observations were correlated with ICDRG grading. ICDRG grading was reassessed following dermoscopic evaluation. Among parthenium reactions, +++ grading predominated (45%, n = 9), followed by ++ (30%, n = 6) and + reactions (20%, n = 4), while doubtful reactions were uncommon (5%, n = 1). Dermoscopy showed clear severity-dependent patterns, with > 50% erythema mainly in ++ and +++ grades and complete erythema largely confined to +++ reactions. Homogeneous erythema and clustered white and translucent globules were characteristic of higher grades. PPD reactions were most frequently graded as ++ (38%, n = 10), followed by + (27%, n = 7), doubtful (23%, n = 6) and +++ reactions (12%, n = 3). Dermoscopically, PPD showed prominent erythema, homogeneous erythema, grey globules (60% of ++ reactions) and frequent follicular obstruction (43% of ++ reactions). Notably, yellow (in parthenium) and black pigmentation (in PPD) was consistently detected dermoscopically but was not appreciable clinically. Overall, seven reactions were clinically graded as doubtful. Dermoscopy enabled reclassification of all, with two (29%) deemed negative and five (71%) upgraded to ICDRG +1. Dermoscopy reveals severity-dependent and antigen­-specific patterns in patch test reactions and aids in resolving equivocal ICDRG grades. Incorporation of dermoscopy as an adjunct to routine patch test interpretation may enhance accuracy in reaction grading and allergen identification.