A skin rash to remember

A 30 year old man presented to the emergency department with a four to five day history of a painful disfiguring rash (fig 1⇓). It started around his mouth but later spread to the rest of his face, as well as his neck and shoulders. He had a history of mild atopic dermatitis, but he had been otherwise well apart from a “cold sore” before the rash appeared. He was not taking any regular drugs, had no allergies, and had not treated the rash with any topical drugs. He was systemically well and the only abnormalities seen on routine blood tests were mild lymphopenia (0.8×109/L, reference range 1-4) with raised C reactive protein 64 mg/L (<0.6;1 mg/L=9.5 nmol/L). HIV testing was negative. ### 1 What is the diagnosis? #### Short answer Eczema herpeticum, with secondary staphylococcal superinfection. This is a dermatological emergency. #### Long answer Possible diagnoses include eczema herpeticum with secondary staphylococcal superinfection, viral xanthems (such as pox viruses), bacterial infection, drug eruption, contact dermatitis, erythema multiforme, or exacerbation of a primary skin disorder. The appearance of the rash is not typical of an isolated flare of atopic dermatitis. The absence of recent use of drugs excludes a drug eruption and the distribution is not consistent with contact dermatitis. Nor are the lesions typical of erythema multiforme. Given the recent history of a cold sore, the appearance of the rash with an initial monomorphic vesicular eruption, and subsequent punched out erosions and impetiginous change, the most likely diagnosis is eczema herpeticum, with secondary staphylococcal superinfection. Eczema herpeticum is caused by herpes simplex virus …