Erythema multiforme in Child
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), mycoplasma pneumonia, group A Streptococcus, and Epstein-Barr virus. Importantly, mycoplasma pneumonia-induced EM is associated with prominent mucositis and absent or sparse cutaneous findings, which, if present, tend to have atypical morphology, including vesicles, bullae, targetoid lesions, and atypical targets / macules. The distinct cutaneous features seen in hypersensitivity eruptions due to mycoplasma pneumonia have led to the term "mycoplasma pneumonia-induced rash and mucositis," or MIRM, which some argue should be used to refer to any severe mucocutaneous eruption associated with mycoplasma pneumonia, abandoning the previous practice of classifying mycoplasma pneumonia-associated eruptions as EM, SJS, incomplete SJS, or mycoplasma pneumonia-associated mucositis.
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
- Urticaria – New lesions appear daily; lesions are transient and last less than 24 hours, associated with edema of lips, face, hands, and feet. No evidence of epidermal damage in the center of urticarial lesions. Subcutaneous epinephrine injections will clear urticarial lesions but not EM lesions.
- 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.
- Mycoplasma pneumonia-induced rash and mucositis (MIRM) – Occurs secondary to mycoplasma infection as evidenced by clinical pneumonia, imaging studies, and/or mycoplasma serologies. 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.
- Kawasaki disease – Children with Kawasaki disease will appear ill and have a fever. Kawasaki disease may be associated with cervical lymphadenopathy, edema of the hands and feet, and significantly elevated inflammatory markers, whereas EM is not.
- Generalized fixed drug eruption – Look for erythematous plaques that develop on the lips, face, distal extremities, and genitalia 1-2 weeks after initial exposure and within 24 hours after subsequent exposure. Oral mucosa can be involved. Histology will differentiate fixed drug eruption from EM.
- Viral exanthem – Target lesions or mucosal involvement should not be present in a viral exanthem, differentiating it from EM.
- Cutaneous small vessel vasculitis – Targetoid lesions may be present, but mucosal surfaces should be spared. Additionally, biopsy will reveal leukocytoclastic vasculitis.
- Polymorphous light eruption – This will typically present with pruritic papules and papulovesicles in a photodistribution. Mucosal sites are spared.
- Arthropod bites (insect bites)
- Molluscum contagiosum
- Erythema annulare centrifugum
- Erythema migrans (Lyme disease)