FIGURE 68.7 This erythematous oval plaque occurred at the identical site where it occurred the last time this patient was exposed to a sulfonamide antibiotic (Reprinted with permission from Goodheart HP Goodheart’s Photoguide of Common Skin Disorders 2nd ed Philadelphia, PA: Lippincott Williams & Wilkins; 2003.) Erythema Multiforme The lesions of EM have a classic target appearance, which appears as a welldefined round macule or papule with three distinct zones: two concentric rings around a dusky, bullous, or crusted center ( Fig 68.8A,B ) The lesions are symmetrically distributed and favor the distal extremities, especially the upper extremities Mucous membrane lesions can be seen in up to half of cases Bullous lesions rupture easily, leaving swelling and crusting ( Fig 68.9 ) EM lesions are fixed, with individual lesions lasting approximately days Systemic symptoms of malaise, low-grade fever, myalgias, or arthralgias may be present EM is a hypersensitivity reaction most often secondary to an infectious trigger EM has been associated with many infectious agents, including bacterial, viral, fungal, and parasitic infections Herpes simplex virus and and Mycoplasma are the most common infectious triggers Medications may be a cause of EM, most commonly sulfonamides, antiepileptic medications, and antibiotics