Erythema multiforme is a hypersensitivity reaction that is most commonly triggered by infections. It may be divided into minor and major forms.

Previously it was thought that Stevens-Johnson syndrome (SJS) was a severe form of erythema multiforme. They are now however considered as separate entities.

Epidemiology: most commonly occurs in young adults (20-40)

Causes

• viruses: herpes simplex virus (the most common cause),
• idiopathic
• bacteria: Mycoplasma, Streptococcus
• drugs: penicillin, sulphonamides, carbamazepine, allopurinol, NSAIDs, oral contraceptive pill, nevirapine
• connective tissue disease e.g. Systemic lupus erythematosus
• sarcoidosis
• malignancy

PC

• target lesions usually <3cm in size, they usually have 3 striking features:

  • A central blister or dusky red area
  • A surrounding pale ring of oedema
  • An erythematous halo in the periphery

• pruritus is occasionally seen and is usually mild

  The more severe form, erythema multiforme major is associated with mucosal involvement.

Site of involvement:

• initially seen on the back of the hands / feet before spreading to the torso
• upper limbs are more commonly affected than the lower limbs