Erythema multiforme

Erythema multiforme (EM) is an immune-mediated inflammatory skin condition associated with several viral infections, that appears with red patches evolving into target lesions, typically on both hands. It is typically associated with infection by either herpes simplex virus or Mycoplasma pneumoniae.

It is a type IV hypersensitivity reaction in which T-lymphocytes target skin keratinocytes due to the presence of specific proteins that resemble antigens of HSV, Mycoplasma, or other pathogens and foreign substances. It is an uncommon disorder, with peak incidence in the second and third decades of life. The disorder has various forms or presentations, which its name reflects (multiforme, "", from + ). Target lesions are a typical manifestation. Two standard types, one mild to moderate and one severe, are recognized (erythema multiforme minor and erythema multiforme major), as well as several rare and atypical types.