A 20-year-old woman presents to the dermatology clinic with a 5-day history of a mildly pruritic rash on both of her legs and feet. She has no pertinent medical history and denies any recent illness or changes in medication preceding the rash onset. The patient reports no fever, chills, nausea, vomiting, diarrhea, sore throat, joint pain, or other systemic symptoms. Review of systems is negative.

Vital Signs and Physical Examination

The patient’s vital signs are within normal limits. Physical examination is notable for nonblanching purpuric papules and small plaques (ranging from 0.2 cm-3 cm) diffusely on her bilateral lower legs and feet (Figure 1). A few plaques have a central annular area darker than the surrounding area. The rash spares her upper legs and the rest of her body. The rest of her physical exam is within normal limits.

A punch biopsy is performed on a lesion on her leg and the patient is sent home with a prescription for topical steroids. The patient returns to the clinic 4 days later because of severely increasing pruritus and change in rash appearance. She reports that the topical steroids have not helped and the rash is worsening. At this point, the lesions on dependent areas (both her ankles and feet) are predominantly bullous targetoid plaques that are darker in color than at her previous visit (Figure 2).

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Laboratory Results

Her initial serologic and laboratory tests are within normal limits. She has a normal complete blood count (CBC), urine analysis with microscopy (UA), erythrocyte sedimentation rate (ESR), kidney function test, and liver function tests (LFTs). Of note, rheumatoid factor (RF) immunoglobulin M is positive.

The initial differential diagnosis involves leukocytoclastic vasculitis (LCV). However, following the second presentation of the rash, LCV seems less likely and possible causes of the rash include bullous diseases such as bullous Sweet syndrome and bullous erythema multiforme.

Punch biopsy reveals superficial and mid-dermal perivascular inflammatory infiltrate consisting of mainly neutrophils with nuclear dust and fibrin within the vessel walls. Numerous extravasated lymphocytes are noted as well (Figure 3).

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