Full thickness epidermal necrosis in the presence of a normal dermis is seen in toxic epidermal necrolysis, a rare immune-mediated disease. Single cell necrosis likely represents apoptosis and is a powerful lesion diagnostically. It is typical of all dermatitis reactions, and only becomes diagnostically useful in those few diseases in which spongiosis is extremely marked. Examples include feline eosinophilic plaque, seborrheic dermatitis, zinc responsive dermatoses and the rarely encountered contact dermatitis. Spongiosis may lead to the formation of spongiform vesicles and pustules.
Intracellular edema has several synonyms.
Ballooning degeneration, originally used to describe the hypereosinophilic, swollen and acantholytic cells of herpetiform vesicles, has been extended to include the swollen and pale keratinocytes of the pox virus diseases. Hydropic degeneration and vacuolar degeneration are used to describe intracellular edema of the basal layer. These lesions are typical of the interface dermatoses to be discussed elsewhere. Severe intracellular edema may result in reticular degeneration and the formation of intraepidermal vesicles. This refers to the loss of cohesion between epidermal cells.