Widespread cutaneous eruption in a patient with atopic dermatitis

This patient in his late teens presented with a one week history of a widespread painful rash, accompanied by fever and fatigue. Two weeks previously he had started oral upadacitinib—a Janus kinase inhibitor—at 15 mg once daily for severe, widespread atopic dermatitis. Physical examination showed numerous vesicles, some with central umbilication, distributed over the neck, anterior trunk, and both upper limbs (fig 1), with no lymphadenopathy. Herpes simplex virus type 1 (HSV-1) infection was detected by polymerase chain reaction (PCR) testing of a swab specimen, confirming the diagnosis of eczema herpeticum. Treatment with upadacitinib was stopped temporarily. The patient was treated with intravenous aciclovir (5 mg/kg three times daily) for seven days because of the severity of symptoms and his intolerance to oral therapy. He also received topical fusidic acid for localised bacterial superinfection. The blisters and fever resolved after one week, leaving post-inflammatory hyperpigmentation.