The cause of pyoderma gangrenosum is unknown, but people who have pyoderma gangrenosum tend to have certain underlying disorders, including inflammatory bowel disease, arthritis, cancers, and blood disorders.
In pyoderma gangrenosum, the immune system seems to be reacting to the skin itself. Unlike many inflammatory skin conditions that are caused by lymphocytes (a type of white blood cell), antibodies (proteins), or both, pyoderma gangrenosum involves abnormal function of another type of white blood cell called neutrophils (see Overview of the Immune System).
Pyoderma gangrenosum typically affects people who are 25 to 55 years old. Pyoderma gangrenosum can develop on areas of skin that have recently been injured or operated on. Thus, areas affected by pyoderma gangrenosum often worsen if they are biopsied (a sample of skin is removed for examination) or debrided (dead tissue is removed to clean the affected area).
Most often, pyoderma gangrenosum begins as a red bump that may resemble a pimple or an insect bite. Less often, it begins as a blister. The bump or blister then becomes an open, painful sore (ulcer) that expands rapidly. The sores have a raised border that is dusky or purple. The sores can grow together to form larger sores. People often are left with scars after ulcers heal. People commonly have fever and a general feeling of illness (malaise).
Pyoderma gangrenosum can also develop at other locations, such as in the abdominal wall around a colostomy or ileostomy opening in people who have inflammatory bowel disease, or on the genitals. In some people with pyoderma gangrenosum, areas other than the skin, such as the bones, lungs, heart, liver, or muscles, are affected.
Doctors diagnose pyoderma gangrenosum by the appearance of the sores and by ruling out other diseases that cause sores to form on the skin. The diagnosis of pyoderma gangrenosum is strongly suggested if the sores worsen after they are debrided.
A sample of skin may need to be removed and examined under a microscope (called a skin biopsy), even though this procedure might worsen the problem temporarily.
Dressings that protect the skin from drying are applied to help heal the sores.
Potent corticosteroid creams or tacrolimus can be directly applied to sores that are new and not deep. Prednisone taken by mouth is given to people severely affected by the disease.
Drugs that suppress the immune system, such as infliximab, adalimumab, and etanercept, are helpful, particularly for people who have inflammatory bowel disease.
Cyclosporine can be very effective, particularly for people whose disease is progressing rapidly. Dapsone, azathioprine, cyclophosphamide, methotrexate, clofazimine, thalidomide, mycophenolate mofetil, and minocycline are other treatment options.
Surgical treatments are typically not done because they may worsen the sores.