Editing Erythema multiforme (section)

{{Short description|Immune hypersensitivity reaction causing rash}}
{{Hatnote|Not to be confused with [[erythema migrans]], despite that both often involve target lesions (but from different causes).}}

{{Infobox medical condition (new)
| name = Erythema multiforme (EM)
| synonyms = 
| image = Erythema multiforme minor of the hand.jpg
| caption = Erythema multiforme minor of the hands (note the blanching centers of the lesion)
| pronounce = 
| field = [[Dermatology]], [[immunology]]
| symptoms = Rash, skin eruptions, fever, mucosal lesions
| complications = 
| onset = 
| duration = 
| types = 
| causes = [[Type IV hypersensitivity]]
| risks = [[Herpes simplex virus]] infection
| diagnosis = 
| differential = [[Stevens-Johnson syndrome]]/Toxic epidermal necrolysis
| prevention = 
| treatment = Corticosteroids, antivirals (HSV-associated cases only)
| medication = 
| prognosis = 
| frequency = 
| deaths = 
}}

'''Erythema multiforme''' ('''EM''') is an [[Immune-mediated inflammatory diseases|immune-mediated]] inflammatory [[cutaneous condition|skin condition]] associated with several viral infections, that appears with red patches evolving into [[target lesion]]s, typically on both hands. It is typically associated with infection by either [[herpes simplex virus]] or ''[[Mycoplasma pneumoniae]]''.<ref name=Weedon2017>{{cite book|last=Johnstone |first=Ronald B.|title=Weedon's Skin Pathology Essentials |url=https://books.google.com/books?id=NTE_DAAAQBAJ|year=2017|publisher=Elsevier |isbn=978-0-7020-6830-0|edition=2nd|page=41|chapter=3. Lichenoid reaction pattern}}</ref><ref name=Andrew2020>{{cite book |last1=James |first1=William D. |last2=Elston |first2=Dirk |last3=Treat |first3=James R. |last4=Rosenbach |first4=Misha A. |last5=Neuhaus |first5=Isaac |title=Andrews' Diseases of the Skin: Clinical Dermatology |date=2020 |publisher=Elsevier |isbn=978-0-323-54753-6 |pages=141–142 |edition=13th |chapter-url=https://books.google.com/books?id=UEaEDwAAQBAJ&dq=Erythema+Multiforme&pg=PA141 |language=en |chapter=7. Erythema and urticaria}}</ref><ref name=":0">{{Cite book |last=Roujeau |first=Jean-Claude |title=Fitzpatrick's Dermatology |last2=Mockenhaupt |first2=Maja |publisher=McGraw-Hill Education |year=2019 |edition=9th |chapter=Chapter 43: Erythema Multiforme}}</ref>

It is a [[type IV hypersensitivity]] reaction in which [[T cell|T-lymphocytes]] target skin [[Keratinocyte|keratinocytes]] due to the presence of specific proteins that resemble [[Antigen|antigens]] of HSV, ''Mycoplasma'', or other pathogens and foreign substances.<ref name=":0" /> 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'', "[[wikt:multiform#Adjective|multiform]]", from ''[[wikt:multi-#Prefix|multi-]]'' + ''[[wikt:forma#Latin|formis]]''). [[Target lesion]]s 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.<ref name=":0" />