Snapshot A 33-year-old male presents to his physician complaining of several red lesions on his palms, back of hands, and on his lips. His past medical history is significant for recurrent herpes. Introduction Hypersensitivity reaction of the skin Common, acute mucocutaneous disease with classic target-shaped lesions with symmetric distribution Divided into erythema multiforme (EM) major and minor major: involves mucous membranes and systemic signs minor: no mucous membrane involvement and no systemic signs Causes most common = infection Herpes simplex virus (most common cause) Mycoplasma pneumonia upper respiratory infections less common = drugs e.g., sulfonamides, β-lactams, phenytoin idiopathic Often affects young adults (18 - 30 years old especially) Distinct from SJS/TEN, which is a more severe mucocutaneous reaction that is usually caused by a medication Presentation Skin raised (papular), target lesions with multiple rings and dusky center (as opposed to annular lesions in urticaria) three concentric zones of color from center to outer ring central dusky/dark area that can be crust or vesicle paler pink or edematous zone peripheral red/dark ring fixed lesions (as opposed to urticaria, in which lesions typically resolve within 24 hours) negative Nikolsky sign (as opposed to SJS/TEN) generally mild burning or itchiness; nontender most commonly involves palms/soles backs of hands and feet extensor aspects of forearms and legs Must also examine mucosal surfaces and eyes oral genital/anal iris May have systemic signs (e.g., fever, prodrome) Evaluation Diagnosis is based on symptoms and clinical history recent history of infection (e.g., herpes or mycoplasma) can aid diagnosis Differential SJS/TEN (flat lesions, tender, always with mucous involvement, + Nikolsky sign) Urticaria (annular lesions) Erythema nodosum Viral exanthems Treatment EM major corticosteroids opthalmology consult if ocular involvement EM minor – usually self-limited supportive care Treat underlying cause if identified oral acyclovir for HSV Prevention Prevention treat chronic herpes infections if recurrent herpes associated-EM oral acyclovir, valcyclovir, or famciclovir as continuous suppressive therapy Complications Usually none associated with EM minor Potential ocular complications with EM major Prognosis Typically self-limited