The ulcers are generally on the lower extremities. While pyoderma gangrenosum may be an isolated finding, it is most often associated with ulcerative colitis or Crohn's disease. The ulcers have ragged bluish-red overhanging edges and a necrotic base. The lesions often start as pustules or tender nodules at the site of trauma, and then they gradually increase in size until liquefaction necrosis occurs and an irregular ulcer develops. The ulcers are often multiple and may cover large areas of the leg.
Histopathologic findings are non-specific.
Healing tends to parallel the activity of the underlying inflammatory bowel disease, and scarring is relatively common.