Erythema multiforme - Anogenital in
In the past, the conditions EM, Stevens-Johnson syndrome (SJS), and toxic epidermal necrolysis (TEN) were considered a continuum, but it is now recognized that EM does not progress to TEN. Therefore, EM is now considered a distinct hypersensitivity eruption, which can be distinguished from SJS/TEN based on the presence of target lesions, papular (rather than macular) atypical target lesions, and an acral distribution.
In adults, the primary trigger for EM is herpes simplex virus (HSV), which is estimated to incite about 90% of cases. In children, important additional triggers to consider include drugs (particularly penicillin), group A Streptococcus, and Epstein-Barr virus among other viruses and bacteria.
Typically, all cutaneous lesions appear within 24-72 hours and persist for 2 weeks before fading. The eruption recurs on repeated exposure to the inciting agent. While HSV is the most common etiology associated with recurrent EM, several viruses have been associated as triggers, too.
L51.9 – Erythema multiforme, unspecified
22972008 – Erythema multiforme, dermal type
- Stevens-Johnson syndrome (SJS) / toxic epidermal necrolysis (TEN) – Histological features may not differentiate EM from SJS/TEN. Clinically, however, look for irregularly shaped, dusky red macular or patch-like lesions on the trunk, face, and palms / soles. A positive Nikolsky sign can be found; there is mucosal involvement, including the eyes, lips, mouth, and genitalia. Look for hemorrhagic crust, bullae, and denudation in these areas. Systemic symptoms are commonly present but not invariable. Lesions are more pronounced on the trunk than on the extremities. Precipitating factors are usually medications.
- Reactive infectious mucocutaneous eruption (RIME) – Usually occurs secondary to mycoplasma infection (as evidenced by clinical pneumonia, imaging studies, and/or mycoplasma serologies) although Chlamydia pneumoniae, human parainfluenza virus 2, rhinovirus, adenovirus, enterovirus, human metapneumovirus, and influenza B virus have more recently been recognized to cause a similar clinical picture. There is pronounced oral and ocular mucositis with absent, spare, or mild cutaneous involvement. Cutaneous lesions are most often tense vesiculobullae. Target or targetoid lesions may be present. Cutaneous lesions do not erode or desquamate as seen in SJS/TEN. (Note: erosion is seen in the genital and perianal skin, which are considered akin to mucosal surfaces.) Nikolsky sign is negative. Acute and convalescent mycoplasma titers may be employed to help to establish this diagnosis in the correct clinical scenario.
- Generalized fixed drug eruption – Look for erythematous plaques that develop on the lips, face, distal extremities, and genitalia 1-2 weeks after medication ingestions. Oral mucosa can be involved. Histology will differentiate fixed drug eruption from EM.
- Lichen planus – Very pruritic, sometimes associated with hepatitis C. Biopsy will differentiate EM from lichen planus.
- Secondary syphilis – Scattered scaling papules and plaques; check rapid plasma reagin (RPR), check for history of primary chancre and systemic symptoms.
- Arthropod bites (insect bites)
- Bullous disorders (eg, bullous pemphigoid or pemphigus vulgaris)
- Paraneoplastic pemphigus