Introduction To Erythema multiforme

Definition: Erythema multiforme (EM) is an acute, self-limited, and sometimes recurring skin condition that is considered to be a type IV hypersensitivity reaction.
Etiology: It occurs in response to medicines, infections, or illness

• Herpes simplex virus (HSV; frequently labialis) is strongly associated but may not be clinically apparent. Other viruses, bacteria (M pneumoniae, Chlamydia, Salmonella, Mycobacterium), and fungi (Histoplasma capsulatum, dermatophytes)
• are also associated. 
• Medications account for <10%; NSAIDs, sulfonamides, antiepileptics, allopurinol, and antibiotics are
• responsible for the majority. 
• Physical factors such as trauma, ultraviolet light exposure, and cold have been reported to elicit EM.

Clinical Features: 

Erythema Multiforme. Symmetric distribution of targetoid macules and plaques. The dusky central zone is more obvious on the left waistline lesions.

• Erythema multiforme (EM) begins with symmetric, erythematous, sharply defined extremity or trunk macules, and evolves into a “targetoid” or “bull’s eye” morphology (a flat, dusky, central area with two concentric, erythematous rings).
• Bullae may appear in the central dusky area (bullous EM).
• The mucous membranes, typically oral, may become involved and raise concern for Steven Johnson Syndrome. 
• The typical targetoid lesions allow a diagnosis to be made clinically (bullae, purpura, and mucosal involvement should prompt a dermatology consultation).
• The rash usually persists for 1 to 4 weeks.

Erythema Multiforme. Wrist, hand, and fingers with typical central dusky centers surrounded by the concentric “bull’s eye” rings.

Classification: The condition varies from a mild, self-limited rash to a severe, life-threatening disease.

• Erythema multiforme minor—typical targets or raised, edematous papules distributed acrally
• Erythema multiforme major—typical targets or raised, edematous papules distributed acrally with involvement of one or more mucous membranes; epidermal detachment involves less than 10% of total body surface area (TBSA)
• SJS/TEN—widespread blisters predominant on the trunk and face, presenting with erythematous or pruritic macules and one or more mucous membrane erosions; epidermal detachment is less than 10% TBSA for Stevens-Johnson syndrome and 30% or more for toxic epidermal necrolysis.

Management: 

• Prevention of HSV recurrences is essential. Antivirals administered after lesions present have minimal clinical impact, but patients should be referred for future prophylaxis consideration.
• Use of facial sunscreens and lip balms may help prevent UVB-induced recurrences. 
• Systemic steroids are discouraged but can be considered in atypical presentations. 
• With the distinctive clinical findings and no systemic symptoms, patients may be discharged home. Systemic symptoms and atypical presentations require admission and dermatologic consultation.

Treatment of mild symptoms may include:

• Medicines such as antihistamines to control itching
• Moist compresses applied to the skin
• Oral antiviral medicine if the reaction is caused by herpes simplex
• Pain medication recommended by your doctor to reduce fever and discomfort
• Topical anesthetics (especially for mouth sores) to ease discomfort that interferes with eating and drinking

Treatment of severe symptoms may include:

• Antibiotics for skin infections
• Corticosteroids to control inflammation
• Treatment in an intensive care or burn care unit for severe cases, Stevens-Johnson syndrome, and toxic epidermal necrolysis (top layer of skin separates from the lower layers)
• Intravenous immunoglobulins (IVIG, an injection of healthy cells from donors into a vein) to stop the disease process