Clues to crack an uncommon clinical conundrum: distinguishing TEN from EMM

Abstract

The clinical challenge of distinguishing toxic epidermal necrolysis (TEN) and Stevens-Johnson syndrome (SJS) from erythema multiforme major (EMM) in a paediatric patient will be one which all dermatologists practising acute dermatology will have encountered in their professional practice. On the one hand, a severe, extensive mucocutaneous disorder, often drug-induced, associated with significant morbidity; on the other, a milder, limited, predominantly infection-induced illness. And yet, the initial clinical presentation of these diseases may be strikingly similar. This month’s issue of the JEADV includes an immensely valuable contribution to the literature on SJS/TEN (together referred to by the authors as Epidermal Necrolysis, EN) in the paediatric population and on the important differential diagnosis in this population of EMM. The cohort size of 62 well-characterized patients in this observational study, drawn from 10 clinical departments, is impressive, allowing for meaningful conclusions to be drawn about the clinical appearance of these patients. The authors clarify the most useful clinical signs for distinguishing EMM, with its more favourable prognosis, from EN. Assessment of the morphology of the target lesions is key, which tend to be predominantly ‘typical’ in the former (maintaining the 3-ringed structure), and more ‘atypical’ in the latter. The extent of body surface area involvement also gives an indication to the type of process, being greater in EN than in EMM. These simple clinical observations can be appreciated by thorough clinical examination, but could also be assessed remotely from highquality clinical images, assisting triage in cases where the patient may be remote from the expert. The study also highlights an important consideration when assessing causality in SJS/TEN in the paediatric population – although predominantly a drug-induced phenomenon in the adult population, the high proportion of so-called idiopathic cases in a paediatric cohort mandates a thorough screen for infectious precipitants. The authors usefully provide in Table 5 a suggested list of investigations which should be completed in all cases of EN and EMM. This is a useful checklist for the practising clinician – if a rigorous approach to detection of infectious precipitants is adopted, this will hopefully lessen the number of paediatric cases wrongly attributed to paracetamol or ibuprofen, rare causes of SJS/TEN. These ‘bystander’ medications are often given in response to the onset of the prodromal coryzal symptoms in SJS/TEN and subsequently mislabelled as causative in the disease process. The finding that histology is not usefully discriminatory between EN and EMM is also useful in the paediatric population; however, this author would contend that a skin biopsy is still an essential investigation to distinguish these disorders from autoimmune blistering disease. This approach is also endorsed by the excellent British guidelines for the management of paediatric SJS/TEN. One possible criticism of the paper is that the nature of reference centres is that they may attract patients with manifestations towards the more severe end of the spectrum, meaning that milder cases of EMM are under-represented. However, the French network of reference centres for the care of patients with skin-loss conditions such as EN is an exemplar in the provision of care for patients with these challenging conditions. The network structure also places the group in a unique position to carry out research on these rare skin diseases, and the authors may be congratulated on this practical and robust contribution to the literature on these disorders.