## Classification by Body Surface Area Involvement **Key Point:** The distinction between SJS and TEN is primarily based on the percentage of epidermal detachment involving the body surface area (BSA), as per the internationally accepted Bastuji-Garin classification. ### Diagnostic Criteria Table | Condition | BSA Involvement | Mucosal Involvement | Systemic Features | |-----------|-----------------|-------------------|-------------------| | SJS | <10% | Common (>90%) | Fever, malaise, arthralgia | | SJS/TEN overlap | 10–30% | Common | Severe systemic involvement | | TEN | >30% | Common (>90%) | Severe; high mortality (25–50%) | **High-Yield:** Option B is correct — SJS involves <10% BSA and TEN involves ≥30% BSA. The 10% and 30% thresholds are the internationally accepted cutoffs used in clinical practice and NEET PG examinations. The intermediate 10–30% range is classified as SJS/TEN overlap syndrome. **Why other options are wrong:** - **Option A (<25% / ≥50%):** These thresholds are non-standard and do not correspond to any accepted classification system. - **Option C (<15% / >15%):** Incorrect thresholds; also illogical as >15% would include the overlap zone. - **Option D (<20% / ≥30%):** The 20% lower threshold for SJS is non-standard; the accepted threshold is <10%. **Clinical Pearl:** Both SJS and TEN present with targetoid lesions and mucosal involvement, but TEN carries significantly higher mortality (25–50%) due to extensive epidermal loss and fluid/electrolyte derangement. Management is supportive, similar to burn care. **Mnemonic:** **SJS-TEN Ladder** — Small (SJS <10%) → Intermediate overlap (10–30%) → Tremendous (TEN >30%). [cite: Fitzpatrick's Dermatology 9e; Bastuji-Garin S et al. Arch Dermatol 1993; Robbins 10e Ch 25] 
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