What causes this persistent rash on her lower extremities?

This otherwise healthy 36-year-old female presented with a 1 month history of an itchy rash confined to both lower extremities. She has been on the same birth control pills for years and denies any other medications, supplements, or recent illnesses.

What's your diagnosis?

A. Insect bites.
B. Shaving folliculitis.
C. Vasculitis.
D. Staphylococcal folliculitis.
E. Yeast folliculitis.

Answer on next page

Answer: Vasculitis

A biopsy confirmed the diagnosis of leukocytoclastic vasculitis (C). Subsequent work up was unremarkable, the patient cleared with a prednisone taper without recurrence. Cutaneous vasculitis is not associated with any internal markers or symptoms. Insect bites, shaving folliculitis, Staphylococcal, and yeast folliculitis would be more papular than seen here. The folliculitis would be centered around follicles unlike what is seen in this patient. In addition, Staphylococcal infections would be expected to be tender rather than itchy. 

In up to 60% of cases of cutaneous necrotizing vasculitis, the cause remains unknown. In has otherwise been attributed to a variety of underlying conditions, such as drugs, chemicals, food allergens, infections, chronic inflammatory systemic disorders, or malignant neoplasms.

Reference

    Tsampau D, Buggiani G, Hercogova J, Lotti T. Cutaneous necrotizing vasculitis: a rational therapeutic approach. Dermatol Ther. 2012;25:335-339.