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| Fig. 64.5 Pyoderma gangrenosum. A, Rapidly expanding classic lesion demonstrating characteristic undermined border. B, Older lesion without an active edge. Note that the depth of the ulcer exposes underlying tendons. (Courtesy of James E. Fitzpatrick, MD.) |
Clinically, the lesions begin as a small papule/pustule that enlarges to form an ulcer. The ulcer has a necrotic center that typically involves the skin and subcutaneous tissues down to muscle, tendons, and fascia (Fig. 64-5). In older lesions, the intact epidermis at the borders of the lesion is erythematous with a purple hue and has a characteristic undermined edge. Another helpful clinical feature is the extreme pain and tenderness of these lesions. There are few cutaneous diseases that approach pyoderma gangrenosum in the severity of lesional pain and tenderness.
Most cases of pyoderma gangrenosum occur without an underlying disease (50%), but this condition has been associated with several systemic diseases, most notably Crohn’s disease (1% to 5%), ulcerative colitis (30% to 60%), leukemias, rheumatoid arthritis, and other collagen vascular disease.
