Symmetrical drug-related intertriginous and flexural exanthema (SDRIFE) is a cutaneous drug eruption with a characteristic distribution of erythema on the gluteal/inguinal region and intertriginous areas with unclear pathogenesis. In this study, we aimed to characterize the T-helper immune phenotype in SDRIFE in comparison with psoriasis and eczema to further the understanding of the pathophysiology and immune response of this rare disorder. Immunohistochemical staining was performed on 9 skin biopsies each from SDRIFE, psoriasis, and eczema using immunohistochemistry for CD3 and dual CD4/T-bet, CD4/GATA3, and CD4/RORC to quantify the percentage of Th1, Th2, and Th17 cells, respectively. A significant difference was detected in the average percentage of Th1 between all 3 groups with the highest percentage of Th1 cells seen in psoriasis, followed by SDRIFE and eczema. SDRIFE showed significantly lower Th2 expression as compared to both psoriasis and eczema. There was a trend towards a higher average percentage of Th17 in psoriasis and SDRIFE, and the ratio of Th17:Th2 was significantly higher in samples of SDRIFE compared with both eczema and psoriasis. The findings characterize SDRIFE as a Th1 and possibly Th17-driven process, which could inform future therapeutic options and substantiate the model of SDRIFE as a delayed-type hypersensitivity reaction.
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