Erythema Multiforme

Key Points
Fairly common skin condition which consisting of “targetoid” or “target-like” lesions
May represent a spectrum of disease, including milder reactions to underlying infection and more severe eruptions due to medications

Erythema multiforme is a fairly common skin condition in which red bumps or blisters appear. They will often enlarge, with necrosis of the skin centrally. This phenomenon causes the lesions to take on a “target” or “bullseye” like appearance. The arms are more commonly affected than the legs, and the palms and soles may be affected as well the face and neck. The condition is classified into minor and major EM, with slightly differing presentations.

Erythema Multiforme major is considered by many to be in the spectrum of Toxic Epidermal Necrolysis (TEN) and is often related to ingestion of certain medications. Cutaneous lesions consist of well-defined red or pink macules (from a few to over 100), which elevate and enlarge, eventually coalescing into large “atypical targetoid” plaques which may darken at the center. These patches or plaques usually develop blisters or crusting, and may be accompanied by itching or burning. The condition may also affect mucosal surfaces such as the lips, eyes, anus, genitals, trachea, GI tract, and mouth. Cases with mucosal involvement typically consist of redness in the affected area, which may develop erosions or ulcerations and are accompanied by swelling and pain. For the diagnosis of EM major, there needs to be less than 30% body surface area involved and less than 2 mucosal surfaces affected.

Erythema Multiforme minor is a hypersensitivity reaction usually attributed to an existing infection, most commonly Herpes simplex virus and mycoplasma pneumonia. Given this fact some clinicians have used the term HAEM (or herpes associated Erythema Multiforme). Other triggers include drug reactions and various other viral and fungal infections. The condition may recur in some cases, presenting as intermittent episodes through the years.

Differential Diagnosis (Other conditions with similar appearance)

Acute Febrile Neutrophilic Dermatosis
Pemphigus, paraneoplastic
Acute Hemorrhagic Edema of Infancy
Staphylococcal scalded skin syndrome
Behcet disease
Stevens-Johnson Syndrome and Toxic epidermal necrolysis
Bullous pemphigoid
Urticarial Vasculitis
Contact Dermatitis, Allergic
Contact Dermatitis, Irritant
Drug eruptions

Diagnosis
Key Points
Diagnosis based on appearance of the affected area
Skin Biopsy will be performed to confirm diagnosis and rule out other conditions

Erythema multiforme is typically diagnosed based on the appearance of the lesions and characteristic skin biopsy findings. The extent of the eruption along with associated factors such as active herpes infection or recent medication additions can often provide clues regarding the etiology.

Treatment
Treatment may not be required, as the condition is sometimes self-resolving
Associated infection, such as that caused by herpes virus, should be treated
In drug induced cases of EM major, the offending agent must be stopped
Careful wound care is important in EM major, occasionally requiring inpatient management
*Systemic steroids are often used in severe cases for inflammation control but their use is somewhat controversial

Mild cases of Erythema Multiforme do not usually require treatment, as the condition is typically benign and self-resolving. However, associated infections, if present, should be treated accordingly. Several treatments may be used to assist in relieving symptoms, including antihistamines, topical corticosteroids, anesthetic and antiseptic mouthwashes. Cases of EM major may require hospitalization, especially in cases with severe mucosal involvement. Recurrent cases are often treated long term with medications such as Acyclovir, Dapsone, or antimalarials.