Toxic epidermal necrolysis (TEN) and Stevens Johnson Syndrome (SJS) are severe 
adverse cutaneous drug reactions that predominantly involve the skin and mucous 
membranes. Both are rare, with TEN and SJS affecting approximately 1or 
2/1,000,000 annually, and are considered medical emergencies as they are 
potentially fatal. They are characterized by mucocutaneous tenderness and 
typically hemorrhagic erosions, erythema and more or less severe epidermal 
detachment presenting as blisters and areas of denuded skin. Currently, TEN and 
SJS are considered to be two ends of a spectrum of severe epidermolytic adverse 
cutaneous drug reactions, differing only by their extent of skin detachment. 
Drugs are assumed or identified as the main cause of SJS/TEN in most cases, but 
Mycoplasma pneumoniae and Herpes simplex virus infections are well documented 
causes alongside rare cases in which the aetiology remains unknown. Several 
drugs are at "high" risk of inducing TEN/SJS including: Allopurinol, 
Trimethoprim-sulfamethoxazole and other sulfonamide-antibiotics, 
aminopenicillins, cephalosporins, quinolones, carbamazepine, phenytoin, 
phenobarbital and NSAID's of the oxicam-type. Genetic susceptibility to SJS and 
TEN is likely as exemplified by the strong association observed in Han Chinese 
between a genetic marker, the human leukocyte antigen HLA-B*1502, and SJS 
induced by carbamazepine. Diagnosis relies mainly on clinical signs together 
with the histological analysis of a skin biopsy showing typical full-thickness 
epidermal necrolysis due to extensive keratinocyte apoptosis. Differential 
diagnosis includes linear IgA dermatosis and paraneoplastic pemphigus, pemphigus 
vulgaris and bullous pemphigoid, acute generalized exanthematous pustulosis 
(AGEP), disseminated fixed bullous drug eruption and staphyloccocal scalded skin 
syndrome (SSSS). Due to the high risk of mortality, management of patients with 
SJS/TEN requires rapid diagnosis, evaluation of the prognosis using SCORTEN, 
identification and interruption of the culprit drug, specialized supportive care 
ideally in an intensive care unit, and consideration of immunomodulating agents 
such as high-dose intravenous immunoglobulin therapy. SJS and TEN are severe and 
life-threatening. The average reported mortality rate of SJS is 1-5%, and of TEN 
is 25-35%; it can be even higher in elderly patients and those with a large 
surface area of epidermal detachment. More than 50% of patients surviving TEN 
suffer from long-term sequelae of the disease.