- Erythema multiforme (EM) is an acute, self-limited mucocutaneous eruption characterized by distinct targetoid lesions on the skin.
- Although classically defined by the presence of target lesions, at various stages of evolution, EM may appear as erythematous macules, papules, vesicles, or bullae.
- EM is considered an immune-mediated reaction, usually to infectious triggers; numerous additional triggers have been reported in the literature.
- Ranges from relatively mild cutaneous disease (EM minor) to severe forms with significant mucosal involvement (EM major)
- Historically viewed as a spectrum of diseases, most authors now regard EM to be a separate entity from Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). SJS and TEN are distinguished from EM by differing patterns of mucocutaneous involvement, precipitating factors, and prognosis.
- Predominantly affects healthy young adults but can affect people of all ages, including young children
- Possible seasonal variation with increased frequency in spring and summer. The more severe form has been reported to occur more frequently in winter.
- Recurrences are common.
- ~90% of cases are caused by an infectious agent, most commonly herpes simplex virus (HSV) or Mycoplasma pneumoniae.
- <10% of cases are secondary to drug exposure. Common culprits include NSAIDs, sulfonamides, antiepileptics, and antibiotics.
- Reported causes are numerous. Rare precipitants include the following:
- Chemical and physical exposures
- Autoimmune disease
- Often, the causative factor is not identified.
- HSV is the major cause of recurrent EM.
- M. pneumoniae is associated with a distinct phenotype in children, characterized by more severe mucosal involvement, particularly oral and ocular, with less severe cutaneous findings. The term Mycoplasma-induced rash and mucositis, (MIRM) has been proposed to describe this particular presentation.
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