The cause is not known.
This disorder begins as small bumps or blisters that become open sores.
The diagnosis is usually based on the appearance of the sores.
Treatment includes dressings, creams, and drugs.

The cause of pyoderma gangrenosum is unknown, but people who have pyoderma gangrenosum tend to have certain underlying disorders, most commonly

Inflammatory bowel disease

Other underlying disorders include

Vasculitis
Rheumatoid arthritis
Leukemia
Lymphoma
Hepatitis C virus infection (see Hepatitis C, Chronic)
Systemic lupus erythematosus
Sarcoidosis
Beh