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DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms) and SCARs (Severe Cutaneous Adverse Reactions) are life-threatening drug-induced hypersensitivity syndromes characterized by widespread skin eruptions and multi-organ involvement. These conditions typically develop 2-8 weeks after drug initiation and carry significant morbidity and mortality if not promptly recognized and treated. Common culprit medications include anticonvulsants, allopurinol, antibiotics, and antiretrovirals.
Both DRESS and SCARs involve delayed-type hypersensitivity reactions (Type IV) mediated by T-cell activation and cytotoxic responses to drug metabolites or the drugs themselves. The pathogenesis involves genetic predisposition (particularly HLA associations), drug metabolism abnormalities leading to toxic metabolite accumulation, and reactivation of latent viruses (especially HHV-6, EBV, and CMV). This results in widespread keratinocyte apoptosis, inflammatory cascade activation, and multi-organ dysfunction through immune-mediated tissue damage.
Early recognition requires high clinical suspicion when patients present with fever, skin eruption, and systemic symptoms weeks after starting new medications. The combination of eosinophilia, atypical lymphocytes, and organ involvement (hepatitis, nephritis, pneumonitis) helps distinguish these conditions from other drug reactions. Immediate drug discontinuation is crucial, as delayed recognition and continued drug exposure significantly worsen outcomes and increase mortality risk from progressive multi-organ failure.