History
Appearance of an unusual rash, usually without itching, particularly in a patient who has herpes simplex.

ALERT
Because it is an immunologic reaction, drug-related erythema multiforme will not occur until 7–14 days after exposure to the offending agent, unless the patient has had the medication previously.

Physical Exam

• Typical pleomorphic eruption is a mixture of macules of various sizes and target lesions. These consist of a central inflamed and superficially necrotic area, surrounded by a halo of less inflamed skin, enclosed within an outer erythematous rim.
  • Purpuric lesions are uncommon, and vesicles may be related to antecedent herpes 1 infections.
  • Rash occurs on the palms, soles, dorsum of the hands, and extensor surface of the extremities and the face; often recurrent, following a viral infection.
• In erythema multiforme there may be involvement of one mucus membrane. This consists of target lesions of the lips or herpetic lesions without extensive necrosis. This may cause confusion with Stevens-Johnson syndrome in which two or more mucus membranes are involved, often with deep ulceration and necrosis.
• Corneal ulceration is a serious complication.