33 Erythema multiforme
Erythema multiforme is an immune-mediated, pleomorphic skin disease that frequently results in erosions and ulcerations over both skin and mucosal surfaces, but can also result in so-called ‘target lesions’ (see ‘Aetiopathogenesis’ section). Clinically, erythema multiforme is classified according to the extent of the skin lesions and mucosal involvement; however, confusion has arisen in the past because erythema multiforme is also a histopathological diagnosis, and the term is used by pathologists whenever the characteristic histological changes are present.
The aetiology is multifactorial and poorly understood. Recognized underlying causes include drug eruptions, infection and internal neoplasia, or disease may be idiopathic. This report describes a case of erythema multiforme, which was thought to have arisen as the result of a recent respiratory infection.
This presentation was unusual and suggestive of an autoimmune or immune-mediated disease. In such cases a thorough history may provide valuable clues as to the underlying cause, if there is one. It is important to establish details such as recent drug therapy, symptoms of systemic illness and evidence of zoonosis or contagion.
The history in this case was as follows:
Apart from target lesions, erythema multiforme can result in many other different skin and mucosal lesions. Skin lesions include erythematous annular and serpiginous configuration of plaques, papules, erosions, collarettes and, in more severe cases, areas of erosion and ulceration. Mucosal lesions consist of vesicles and bullae progressing to erosions and ulceration. The axillae and groin, the mucocutaneous junctions, the oral cavity, the pinnae and the footpads are reported to be the most frequently affected areas.
Clinical examination in this case revealed:
Figure 33.2 Macular erythema and erosions over the buccal mucosa. A bullous lesion is evident (arrowed).
The differential diagnoses for erythema multiforme are extensive due to the multiple lesions types that are encountered in this condition. They include urticaria, pyoderma, dermatophytosis, demodicosis and some of the bullous autoimmune diseases, such as pemphigus vulgaris, bullous pemphigoid and epidermolysis bullosa acquisita. More severe lesions with larger areas of erosion or ulceration would need to be differentiated from burns, toxic epidermal necrolysis and vasculitis.
The list of possible differential diagnoses in this case included: