A deep skin ulcer with a well defined border, which is usually violet or blue. The ulcer edge is often undermined (worn and damaged) and the surrounding skin is erythematous and indurated. The ulcer often starts as a small papule or collection of papules, which break down to form small ulcers with a so called cat's paw appearance. These coalesce and the central area then undergoes necrosis to form a single ulcer. [PMID:16858047]
