Pyoderma gangrenosum (pie-oh-DER-muh gang-ruh-NO-sum) is a rare condition that causes large, painful sores (ulcers) to develop on your skin, most often on your legs.
It’s not certain what causes pyoderma gangrenosum, but it appears to be a disorder of the immune system. People who have certain underlying conditions, such as inflammatory bowel disease or rheumatoid arthritis, are at higher risk of pyoderma gangrenosum.
Treatment typically includes high doses of corticosteroids, such as prednisone, along with other drugs designed to suppress your immune system. It can take weeks or even months to heal the ulcers associated with pyoderma gangrenosum.
The cause of pyoderma gangrenosum isn’t well understood. It’s often associated with inflammatory conditions, such as ulcerative colitis and Crohn’s disease. If you have pyoderma gangrenosum, new skin trauma, such as a cut or puncture wound, may result in the formation of new ulcers. This tendency of new ulcers to form from trauma, including surgery, is known as pathergy.
Pyoderma gangrenosum usually starts with a small, red bump on your skin, which may resemble a spider bite. Within days, this bump can develop into a large, painful open sore. The ulcers usually appear on your legs, but may develop anywhere on your body. If you have several ulcers, they may grow and merge into one larger ulcer.
When to see a doctor
Talk to your doctor if you develop unexplained blistering on your skin, an itchy rash or a sore that’s slow to heal.