Journal of Cutaneous Medicine and Surgery 1–5 © The Author(s) 2016 Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1203475416639018 jcms.sagepub.com Introduction There is still widespread confusion regarding the clinical presentation, aetiology, and diagnostic criteria of erythema multiforme (EM), in particular EM major (EMM) and Stevens-Johnson syndrome (SJS), in paediatric patients. Previous literature has considered EMM and SJS inter- changeably or as “variants” of each other. 1 In a large pro- spective study, Auquier-Dunant et al 2 brought clarity to these entities, separating them on the basis of the underlying aeti- ology and clinical presentation into EMM, SJS, SJS and toxic epidermal necrolysis (TEN) overlap, TEN, and unclas- sified EMM or SJS. Patients with EMM were younger (median age, 24 years), presented with fever, often had involvement of 2 or more mucous membranes, and had typi- cal or atypical acrally distributed target lesions affecting <10% of the body. 2 Herpes aetiology was present in 46% of patients with EMM, while Mycoplasma pneumoniae was noted in only 3% of cases. 2 Our clinical experience suggested that M pneumoniae is more commonly seen in the paediatric population presenting with EMM, particularly a phenotype characterized by atypi- cal target lesions with central blistering. Given implications for management and prognostication, our objective was the determine if this presentation is more indicative of underly- ing M pneumoniae infection by examining a retrospective cohort of patients labeled as having EMM or SJS. Methods This was a retrospective cohort study conducted at the Hospital for Sick Children in Toronto, a tertiary academic centre. The study received the institution’s ethics board approval. The data were collected from the electronic charts of patients admitted from June 1999 to July 2013. The inclusion criteria were age 3 months to 18 years and a discharge diagnosis of EM minor, EMM, or SJS. Children with diagnoses of TEN were excluded from our study because it was felt that the primary confusion lies in the distinction between EMM and SJS. Data collected included prodromal symptoms such as fever, sore throat, cough, and respiratory distress; time from prodromal symp- toms to skin presentation and diagnosis; medications prior to presentation; appearance and distribution of rash; number of mucous membranes involved; aetiological laboratory investi- gations; treatment; and prognosis. The case definitions used for EM minor, EMM, and SJS were as follows: for EM minor, abrupt onset of acrally Original Article 639018CMS XX X 10.1177/1203475416639018Journal of Cutaneous Medicine and SurgeryLangley et al research-article 2016 1 The Hospital for Sick Children, Toronto, ON, Canada 2 St Joseph Hospital, Toronto, ON, Canada 3 University of Toronto, Toronto, ON, Canada Corresponding Author: Elena Pope, MD, The Hospital for Sick Children, Division of Paediatric Medicine, 555 University Avenue, Toronto, ON M5G 1X8, Canada Email: elena.pope@sickkids.ca Erythema Multiforme in Children and Mycoplasma pneumoniae Aetiology Annie Langley 1 , Niloofar Anooshiravani 1 , Sarah Kwan 1 , Jeanne Zeller 2,3 , and Elena Pope 1,3 Abstract Erythema multiforme (EM) in children is understudied and confused with Stevens-Johnson syndrome (SJS) despite their being separate diseases with unique aetiologies and clinical presentations. The goal of this study was to determine the prevalence of Mycoplasma pneumoniae in paediatric patients with EM minor, EM major (EMM), and SJS. This retrospective cohort at The Hospital for Sick Children accrued all cases of EM minor, EMM, and SJS from 1999 to 2013. Sixty-five cases were identified: 20 of EM minor, 23 of EMM, and 22 of SJS. Aetiologies were attributed in 58% of cases: 79% infection and 21% drug aetiology. Sixty-one percent of patients with EMM were M pneumoniae positive, compared with 14% of those with SJS and 22% of those with EM minor (P < .01). M pneumoniae patients were older at presentation (P = .03) and more frequently had sore throat (P < .01) and atypical targets with central blistering (P < .01). These findings suggest that M pneumoniae should be suspected and treated until laboratory confirmation becomes available in patients presenting with atypical target lesions with central blistering. Keywords paediatric dermatology, erythema multiforme, Mycoplasma pneumoniae