Consists of well-circumscribed target-like lesions most commonly on the extremities. In about half of cases the cause is never found. Causes include:
- Herpes simplex virus
- Mycoplasma pneumoniae
- Hepatitis B
- Lupus erythematosus
- Drugs such as salicylates, penicillin, barbiturates.
Note how some causes are the same as erythema nodosum. Blistering can occur. EM can be thought of as on a clinical spectrum with Toxic Epidermal Necrolysis and Stevens Johnson syndrome at the extreme end, although the underlying pathology appears to be different.
There is no clear evidence that steroids help in erythema multiforme. Treatment is symptomatic support.