Erythema multiforme (EM) is a hypersensitivity reaction which tends to develop abruptly. Usually it will disappear on its own, but sometimes treatment may be required for the symptoms. It occurs in all racial groups and is predominantly observed in young adults (20-40 years), but can occur in any age group. The condition is slightly more common in men.
Erythema multiforme is characterised by the sudden development of few to hundreds of red papules (spots). The papules usually begin over the back of the feet and hands, and spread upwards towards the trunk. The face is often involved. The hands and arms are more commonly affected than the feet and legs. Over time these papules evolve to plaques (raised patches) and then typical target shaped lesions. These target lesions have a dusky red centre, a paler area around this, and then a dark red ring round the edge. Sometimes the centre of the target can be crusted or blistered. The targets can be different shapes and sizes, hence the latin name: erythema (redness) multi (many), forme (shapes).
Erythema multiforme is usually mild - 'erythema multiforme minor' – with only skin involvement, causing little trouble and clearing quickly. There is also a rare but more severe type, 'erythema multiforme major', which has similar skin features to EM minor, but additionally there is involvement of one or more mucosal membrane (e.g. the lips, the inside of the mouth, the windpipe, the gullet, the anus or genital area, and the eyes) and usually some associated symptoms, such as fever or joint pain.