They are characterised by irregular purpuric macules with occasional blistering and most patients also have extensive mucosal involvement.
Although the appearence may initially seem similar to erythema multiforme (ableit more severe) histologically they are different:
- erythema multiforme - cell-rich infiltrate, lots of T lymphocytes
- SJS/TEN - cell-poor infiltrate, macrophages and dendrocytes
The difference between SJS and TEN is arbitrarily defined as SJS involves <10% body surface while TEN involves >30%.
The commonest cause of SJS/TEN is medication, with sulphonamides being the most commonly implicated drug.
Other drug precipitants include:
- phenytoin
- carbamazepine
- barbituates
- allopurinol
- penicillin
- NSAIDs
The commonest time for SJS/TEN to develop is 9 to 14 days after starting a new drug.
Infections can also cause SJS/TEN.
In addition to the rash patients are systemically unwell and have a + Nikolsky's sign.
Management is:
- stop precipitating drug
- often ITU
- IV IG
- ?immunosupression ?plasmophoresis
