Influence of Atopic Dermatitis on the Dermoscopic Phenotype of Positive Patch Test Reactions: A Prospective Comparative Study.

Atopic dermatitis (AD) may alter the morphology of clinically positive allergic patch test reactions due to epidermal barrier dysfunction and a chronic inflammatory background, thereby complicating routine clinical interpretation. This prospective observational study aimed to evaluate the dermoscopic features of clinically positive allergic patch test reactions and compare their phenotypic expression in patients with and without concomitant AD. Consecutive patients undergoing routine patch testing were screened, and clinically positive reactions (1+, 2+, or 3+ according to ICDRG criteria) were subjected to dermoscopic assessment at scheduled readings. A total of 160 participants were included. Patch test reactions in patients with AD exhibited a consistent dermoscopic pattern, characterized by an increased frequency of perifollicular erythema, yellowish areas, and pigment residuals, whereas homogeneous erythema demonstrated limited discriminatory value in both pediatric and adult populations. Yellowish areas were additionally associated with greater AD severity. These findings suggest that AD may modify the phenotypic expression of clinically positive allergic patch test reactions, particularly when evaluated using dermoscopy. This non-invasive diagnostic tool may provide adjunctive morphological support for patch test interpretation, especially in equivocal cases.