Erythema multiforme

Erythema multiforme (EM) and correlated disorders (Stevens-Johnson syndrome, toxic epidermal necrolysis and Lyell’s syndrome) are immune-mediated, muco-cutaneous conditions, which are characterised by a wide range of clinical symptoms with varying degrees of severity. EM mainly affects young adults as teenagers or young adults; 20% of cases concern children. It heals spontaneously and is characterised by a hypersensitive reaction which can commence with the depositing of immune complexes (mostly IgM) on the walls of the superficial microvasculature of the skin and mucous membranes (with subsequent activation of the complement, vasculitis and ischaemic/apoptotic necrosis of the overlying epithelium). A second characteristic is a cell-mediated, immune response (with a cytotoxic action on the keratinocytes and subsequent formation of sub-epithelial and intraepithelial vesicles/blisters, which subsequently result in ulcers). There are numerous pharmacological and/or chemical agents which stimulate such immune-mediated reactions. On the basis of the extent of the lesions, two clinical forms of EM can be distinguished: minor and major.
EM minor marginally involves the skin and a single mucosal site; it can heal spontaneously or recur. The involvement of the skin in the minor variant is characterised by: targetoid lesions of EM, itchy and well-defined borders (characterised by central portion of epidermal necrosis, surrounded by a lighter, edematous ring with an erythematous zone on the extreme periphery); atypical lesions (rounded in shape, edematous and palpable, similar to typical lesions but with only two areas and/or poorly-defined borders ) and bullous lesions.
EM major is characterised by a more widespread involvement of the skin and mucosa. Of the latter, the oral cavity is usually affected with the presence of – in more than 50% of cases – ulcerative lesions which can also involved the oral mucosa.
A differential diagnosis includes: stomatitis, pemphigoid, vesicular-bullous, immune-mediated and sub-epithelial lesions (mucous membrane pemphigoid) and toxic epidermal necrolysis.
Diagnosis is usually performed clinically; no specific diagnostic tests exist. A histo-pathological examination and immunofluorescence may be of assistance in distinguishing EM from other pathologies, even if the former is extremely variable. In order to treat EM, it is necessary to eliminate the causal agent, ensure effective oral hygiene (using a chlorhexidine mouthwash without alcohol, tissue-regenerating sprays/gels), suspend acidic foods (by means of a specific diet) and prescribe topical and/or systemic corticosteroids.