Erythema multiforme is an acute immune reaction of the skin, most often triggered by herpes simplex virus and less often by Mycoplasma or medicines. It causes target-shaped lesions, usually on the hands and arms, and settles on its own, but it can return with new herpes outbreaks.
Key symptoms
- Sudden rash of round red spots on the hands, feet, arms and legs
- Mild itch or burning
- Painful mouth sores in the major form
- Recent cold sore, respiratory infection or new medicine
What you find on exam
- Typical target lesions with three zones: dark or blistered center, pale ring, red outer ring
- Symmetric spread on the hands, palms and outer limbs, then toward the trunk
- Check the mouth, eyes and genitals for erosions
- Less than 10 percent of body surface involved, with little skin detachment
Tests
- Clinical diagnosis
- HSV PCR from a cold sore if present
- Mycoplasma testing and chest X-ray if there is cough or other respiratory symptoms
- Skin biopsy if the diagnosis is unclear or Stevens-Johnson syndrome is possible
Treatment basics
- Treat the trigger: stop any suspected drug, treat Mycoplasma if present
- Topical corticosteroids and oral antihistamines for skin symptoms
- Mouth care: anesthetic and antiseptic mouth rinses, plenty of fluids
- Severe mucosal disease: a short course of oral prednisone
- Recurrent herpes-related cases: daily suppressive valacyclovir or acyclovir
Red flags
- Widespread blistering or skin peeling (consider Stevens-Johnson syndrome)
- Eye pain, redness or vision changes (urgent eye referral)
- Mouth sores that stop the patient from eating or drinking
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Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.