A self-limiting hypersensitivity reaction affecting the skin and occasionally mucous membranes.
50% of cases have no obvious underlying cause. Aetio-logical agents include:
Herpes simplex in 33% of cases; may cause recurrent attacks.
Other infections, e.g. vaccinia, orf, streptococci, tuberculosis, histoplasmosis.
Drugs, e.g. sulphonamides, penicillin, phenytoin, barbiturates and carbamazepines.
Connective tissue disorders, such as systemic lupus erythematosus.
Lesions are pinkish red erythematous papules/plaques with central clearing or concentric rings (target lesions). Distribution is usually symmetrical affecting the backs of limbs, hands and feet. Disseminated rash with mucosal involvement with conjunctivitis and necrotic mucosal ulcers is termed Stevens–Johnson syndrome. This is often associated with systemic symptoms.
The withdrawal of any causative drug and treatment of any associated infection is essential. Short courses of oral steroids are sometimes used but their efficacy and safety are unclear. Patients with recurrent erythema multiforme resulting from herpes simplex can be prevented with prophylactic aciclovir.
Disease is usually self-limiting clearing in 2–3 weeks but death can occur with Stevens–Johnson syndrome.