Stevens-Johnson syndrome or toxic epidermal necrolysis

**Definition:** A spectrum of severe and life-threatening hypersensitivity disorders affecting skin and mucous membranes, most commonly precipitated by an idiosyncratic reaction to medication. Stevens-Johnson syndrome (SJS) always involves mucosal surfaces but the skin involvement is limited by definition to <10% body surface area (BSA). Toxic epidermal necrolysis (TEN) may sometimes spare mucous membranes but skin involvement is by definition >30% BSA. An intermediate form is recognised in which mucosal involvement is accompanied by skin involvement of 10-30% BSA (SJS-TEN overlap syndrome). All forms result in extensive sloughing and ulceration and carry a significant risk of fatal outcome.