Stevens-Johnson syndrome and toxic epidermal necrolysis Quiz: Ace Your Exams

An 87-year-old woman presents to the emergency department from an assisted living facility for evaluation of a rash. The patient’s nurse from the facility reports the patient has had flu-like symptoms for the past two days and that today she noticed a desquamating truncal rash that progressed to involve all extremities. The patient has a past medical history of Alzheimer dementia, hypertension, diabetes, and recurrent urinary tract infections. Current medications include hydrochlorothiazide and metformin. Three weeks ago, she was treated with sulfamethoxazole-trimethoprim after she developed a urinary tract infection that was resistant to ciprofloxacin. Temperature is 39°C (102.2°F), blood pressure is 97/60 mmHg, pulse is 110/min, respiratory rate is 18/min, and oxygen saturation is 94% on room air. On physical examination, the patient appears ill and is unable to provide further clinical history. She has conjunctival erythema and oral lesions. Skin examination is notable for the findings shown below. Which of the following tests will lead to a definitive diagnosis?


 Reproduced from: wikipedia