Definition:

Erythema multiforme (EM) is an immune-mediated, mucocutaneous condition characterized by "target" lesions. Classically, EM has been separated into 2 subgroups, EM minor and EM major. In EM minor, lesions often present as papules, which might enlarge and eventually form the typical target lesion with erythema surrounding an area of central clearing. The rash in EM minor preferentially affects the limbs, specifically the extensor surfaces, however, it can also be seen throughout the body, excluding mucous membranes. EM major has mucous membrane involvement. The oral mucosa is most commonly affected, initially with edema that progresses to superficial erosions. Other surfaces that might be involved include the anogenital, ocular, and nasal mucosa. Although previously thought to be on a similar continuum of EM, and histologically appearing the same, Stevens-Johnson syndrome (SJS) is increasingly being considered a separate disease process. It is currently believed that EM is a result of an immune reaction to an inciting infectious or pharmacologic antigen. The most common infectious organisms in EM are herpes simplex virus types 1 and 2, as well as Mycoplasma pneumonia. The first line of treatment for EM is removal of the inciting factor when possible. Systemic steroids have been suggested as adjuvant therapy based on their immunosuppressant effects. To date, their use has been limited to EM major, as EM minor is self-limited.