Immunological and Inflammatory Characteristics of Severe Cutaneous Adverse Drug Reactions: A Retrospective Study

Background: Severe cutaneous adverse drug reaction (SCADR) is a life-threatening immune-mediated disorder, yet humoral immune markers and inflammatory biomarkers have not been systematically characterized across major SCADR phenotypes.This study aims to identify the immunological and inflammatory characteristics of SCADR.Methods: We retrospectively enrolled 60 SCADR patients (2015-2024) and two control cohorts (60 mild drug eruption patients and 60 age-and sex-matched healthy subjects).Baseline serum IgG, IgA, IgM, complement C3/C4, C-reactive protein (CRP), and procalcitonin (PCT) were measured prior to treatment, and between-group comparisons, correlation analyses, and subtype analyses [Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) vs DRESS] were performed.Results: SCADR patients had lower IgG (8.84.1g/L) and complement levels (C3 1.010.37g/L;C4 0.210.12g/L)than controls (P<0.05),alongside markedly elevated CRP (median: 31.1mg/L) and PCT (0.68g/L) (P<0.001).PCT was higher in SJS/TEN than drug reaction with eosinophilia and systemic symptoms (DRESS) (0.85 vs 0.45g/L, P=0.04), whereas eosinophil counts were higher in DRESS.C3 correlated positively with CRP (r=0.60,P<0.001).No significant associations were observed between immunoglobulins and PCT, and PCT and CRP were largely independent.Conclusion: SCADR is associated with concurrent alterations in humoral immune markers and acute-phase inflammatory biomarkers.Differences in biomarker patterns between SJS/TEN and DRESS may help with early clinical phenotyping.Prospective multicenter studies are needed to validate these findings and clarify their clinical significance subsequently.