The recent article by Assier et al1 that appeared in the May 1995 issue of the Archives provides a helpful method by which one may differentiate between the causes of erythema multiforme and Stevens-Johnson syndrome based on the appearance and distribution of cutaneous lesions. Lesions that are predominantly raised and distributed on the extremities and/or the face are usually caused by herpes simplex, while those lesions that are flat and widely distributed or on the torso are caused by drugs.
Unfortunately, the authors use the same characteristics as diagnostic criteria for erythema multiforme and Stevens-Johnson syndrome. This unconventional method of classification ignores the important clinical differences between the two diseases that form the basis for the classic criteria used to distinguish between these diseases. Namely, these criteria are that Stevens-Johnson syndrome is associated with systemic symptoms and involvement of internal organs, whereas erythema multiforme is not.
Bystryn J. Erythema Multiforme With Mucous Membrane Involvement and Stevens-Johnson Syndrome Are Clinically Different Disorders. Arch Dermatol. 1996;132(6):711. doi:10.1001/archderm.1996.03890300141023