📋 Stepwise Approach to Severe Cutaneous Adverse Reactions (SCARs)
🔑 Key Principles — Nelson 686.2
• DRESS (DIHS): onset 2‑6 weeks after drug; fever, rash (morbilliform → erythroderma), facial edema, lymphadenopathy, eosinophilia, atypical lymphocytosis, hepatitis, nephritis, pneumonitis, myocarditis. Mortality ~10%. Latent HHV‑6 reactivation.
• Serum sickness‑like reaction (SSLR): 10‑14 days after drug (cephalosporins, penicillins, minocycline). Urticarial/annular plaques with violaceous center, fever, arthralgia, lymphadenopathy. NO immune complexes (unlike true serum sickness).
• AGEP: hours to days after drug (aminopenicillins, macrolides). Fever, dozens of nonfollicular sterile pustules on edematous erythema, intertriginous onset, desquamation. Neutrophilia.
• Fixed drug eruption (FDE): minutes to hours after drug; solitary or few round dusky red/violaceous patches, recur at same site upon re‑exposure. Resolves with hyperpigmentation.