Lyell syndromeLyell syndrome is a severe reactive dermatitis also known as toxic epidermal necrolysis (TEN). It is traditionally described in the erythema multiforme group of dermatitides. The group includes the continuum of erythema multiforme, Stevens-Johnson syndrome, and Lyell syndrome/TEN. Erythema multiforme is the least severe of the three disorders while Lyell syndrome represents the most severe reaction. Stevens-Johnson syndrome is intermediate in severity. While the three conditions are pathogenetically distinct, there is no reliable feature that would allow to distinguish between them based on morphology alone.
Lyell syndrome usually develops as a reaction to a recent drug exposure. Morphologically, Lyell syndrome is characterized by interface dermatitis and severe diffuse epidermal necrosis. The latter involves the full thickness of the epidermis with sloughing and subepidermal blistering. The epidermal necrosis is by definition diffuse, occupying greater than 10 percent of the skin surface.