A 32-year-old woman with a rash and mucosal erosions

A 32-year-old woman presents to the emergency department with a 3-day history of a widespread rash that started on her face and trunk and spread to the limbs. She also reports fever, sore throat, and painful red eyes. On examination, she is febrile (39.0°C) and has a diffuse, erythematous maculopapular rash with areas of blistering and skin detachment. The skin detachment involves less than 10% of the body surface area. Her lips are swollen and crusted, and there are painful erosions on the oral and vaginal mucosa. Nikolsky's sign is positive. There is bilateral conjunctival injection.

Her medical history includes a recent diagnosis of epilepsy, made 3 months ago. She was started on lamotrigine 25 mg once daily, increased to 50 mg once daily after 2 weeks, and then to 100 mg once daily after another 2 weeks. She has been taking 100 mg daily for the past 2 weeks. She also takes sodium valproate 500 mg twice daily, started at the same time as the lamotrigine. She has no known drug allergies and takes no other medications.

Blood tests on admission show a mild rise in liver transaminases (ALT 120 U/L, AST 90 U/L), C-reactive protein 40 mg/L, and white blood cell count 12,000/µL with an eosinophil count of 1,000/µL. A skin biopsy from an area of blistering shows full-thickness necrosis of the epidermis with subepidermal bullae, consistent with Stevens-Johnson syndrome.

She is admitted to the intensive care unit. Both lamotrigine and sodium valproate are stopped. Over the next 5 days, the skin lesions stop progressing, the fever resolves, and the mucosal erosions begin to heal.