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 login to view 3 more bullets less common = drugs login to view 1 more bullet 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) login to view 4 more bullets 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 login to view 3 more bullets 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 login to view 1 more bullet Complications Usually none associated with EM minor Potential ocular complications with EM major Prognosis Typically self-limited