6th July 2023

Erythema Multiforme (EM)

EM is a self-limiting hypersensitivity reaction caused predominantly by infection, for which HSV causes the majority of cases. Other causes include certain medications or conditions (table 7). It is now considered a distinct entity from Stevens-Johnson syndrome and Toxic Epidermal Necrolysis.

Table 7: Triggers for erythema multiforme

Mycoplasma pneumoniae is often listed as a cause of EM, however this has recently been classified as its own distinct entity, mycoplasma pneumoniae-induced rash and mucositis (MIRM).

EM acutely manifests on the distal extremities as symmetrical erythematous papules that transform into target-like lesions. These have a dusky centre, a pale and oedematous intermediate ring and an erythematous outer ring. Lesions may be painful or itchy. EM minor has cutaneous manifestations only, whereas EM major has the addition of mucosal involvement. Diagnosis is clinical but investigations to review the cause may be required. Treatment is supportive. Precipitating factors should be managed and offending medication avoided. Ocular involvement requires ophthalmology input. Recurrent cases may benefit from antiviral therapy.

Cutaneous erythema multiforme

Image Source: Wikimedia Commons (2011). Erythema Multiforme EM 01 ajustement niveaux auto, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Erythema_Multiforme_EM_01_ajustement_niveaux_auto.jpg (Accessed on: 10 March 2022).

Mucosal erythema multiforme

Image Source: Wikimedia Commons (2021). Erythema multiforme tongue, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Erythema_multiforme_tongue.jpg (Accessed on: 10 March 2022).