36 Ulcers and erosions: Erythema multiforme, toxic epidermal necrolysis and Stevens-Johnson syndrome
Definition: Erythema multiforme (EM) is a mucocutaneous condition mediated by antigen-antibody (immune complex – mainly IgM) deposition in the superficial microvasculature of skin and mucous membranes.
Prevalence (approximate): Uncommon.
Age mainly affected: Younger adults in second and third decades.
Gender mainly affected: M > F.
Etiopathogenesis: There may be a genetic predisposition, with various HLA associations (e.g. patients with extensive mucosal involvement may have HLA-DQB1*0402). A putative immunological hypersensitivity reaction usually to various micro-organisms or drugs (Figure 36.1) (Table 36.1), results in immune complexes and the ingress of cytotoxic CD T lymphocytes, inducing keratinocyte apoptosis and satellite cell necrosis (Figure 36.2).
EM minor (accounts for 80%) is a mild, self-limiting rash usually affecting one mucosa. EM major is a severe, life-threatening variant that overlaps with toxic epidermal necrolysis (see below) and involves m/>