A 32-year-old woman presents to the emergency department for evaluation of a worsening rash that begins at her navel and continues down both of her legs. The rash first appeared approximately 10 days earlier and has gotten progressively worse; initially the rash was itchy, but now is painful. The patient is not receiving any medications and denies recent travel. She has not had a fever or other medical complaints, and has never experienced a rash like this before. She has a dog and 2 cats in her home.

The patient’s vital signs and physical examination are normal except for the rash (Figure). Differential diagnosis includes flea bites with a severe allergic reaction, vasculitis, disseminated gonorrhea, and necrotic erythema multiforme (EM). Laboratory testing (complete blood count, basal metabolic panel, and liver function test) are all normal.

What is the next best step in treatment?

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