Overview of Stevens Johnson Syndrome (SJS), Toxic Epidermal Necrolysis (TEN), and Erythema Multiforme (EM)

• SJS and TEN are basically the same disorder, but different spectrum of disease.   It is an idiosyncratic reaction (usually to drugs) that leads to erythematous skin lesions that progress to epidermal necrosis and sloughing, with mucous membrane involvement, often with a prodrome of fever and influenza-like symptoms.  SJS is when <10% of body surface area (BSA) is involved, TEN is >30% BSA, and 10-30% = SJS/TEN Overlap syndrome.
• EM can be divided into EM Minor and Major, distinguished by involvement of mucosa in EM Major.  Previously, EM Major was thought to be SJS, but new thinking is that they are different diseases with different causes and pathophysiology.  The vast majority (>90%) of EM is caused by infections, particularly herpes viruses (as opposed to SJS/TEN - majority caused by drug reactions).  Unlike SJS/TEN, EM typically has a more benign course. 

(Chanu Rhee MD, 8/31/10)