Pyoderma gangrenosum (pie-o-DUR-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.
No one knows exactly 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.
The ulcers of pyoderma gangrenosum can develop quickly. They usually clear up with treatment, but scarring and recurrences are common.
Pyoderma gangrenosum care at Mayo Clinic