Stevens-Johnson syndrome (SJS) is distinct from toxic epidermal necrolysis (TEN) primarily by the percentage of body surface area with epidermal detachment. The defining parameter and the most common triggering drug class are:

• A SJS: <10% BSA; TEN: >30% BSA; most common trigger: NSAIDs
• B SJS: <15% BSA; TEN: >40% BSA; most common trigger: allopurinol alone
• C SJS: <5% BSA; TEN: >20% BSA; most common trigger: penicillins
• D SJS: <10% BSA; TEN: >30% BSA; most common trigger: sulfonamides and aromatic anticonvulsants ✓

Explanation

SJS/TEN classification (SCARs spectrum): SJS = <10% BSA epidermal detachment; SJS-TEN overlap = 10-30%; TEN = >30% BSA. The most common triggering drugs are sulfonamides (cotrimoxazole) and aromatic anticonvulsants (phenytoin, carbamazepine, lamotrigine, phenobarbital). Allopurinol is the most common cause of TEN in some populations (especially Asian patients with HLA-B*5801). Management includes early drug withdrawal, IVIG, ciclosporin, and SCORTEN scoring for prognosis. NSAIDs (especially oxicam NSAIDs) are also implicated but are not the most common class overall. Penicillins are more commonly associated with DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms).

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.