Histopathologic Features of Drug Reaction With Eosinophilia and Systemic Symptoms.

Importance: Drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome is a severe cutaneous adverse reaction occurring 2 to 8 weeks after medication initiation. Diagnosis is clinical; RegiSCAR scoring includes biopsy "suggestive of DRESS," undefined in the literature.

Objective: This study correlates DRESS dermatopathology, culprit drugs, disease course, and outcome severity compared with maculopapular drug reactions (MDR).

Methods: Between 2014 and 2023, a retrospective cohort study at a tertiary care institute reviewed 55 patients with DRESS, assessing demographics, culprit drug, illness course, and histopathology. Biopsies of 15 patients with DRESS and 15 MDR patients were graded by a predefined histopathological scoring system. Statistical analysis (significant P -value<0.05) included the Fisher exact probability, ANOVA, and correlation tests.

Results: Among 55 patients with DRESS (mean age 50.13, 28 female/27 male), 15 (mean age 50.4, 7 female/8 male) had diagnostic biopsies. Compared with MDR patients, patients with DRESS exhibited significantly more interface dermatitis ( P = 0.04), lichenoid dermatitis ( P = 0.0007), pigment incontinence ( P = 0.04), and periadnexal interface dermatitis ( P = 0.002). MDR biopsies displayed perivascular inflammation and higher eosinophils than DRESS, trending toward significance.

Conclusions: Key histopathologic features are interface dermatitis, periadnexal interface dermatitis, lichenoid dermatitis, pigment incontinence, and neutrophils dominance over eosinophils indicate DRESS clinically.