Pyoderma gangrenosum: causes, symptoms and treatment

The NHS says it is not always clear what causes pyoderma gangrenosum, that it may be an autoimmune disease, and that it can also sometimes happen after an injury to the skin. The dermatologists say that in about half of people there is no known cause, and that in some cases it may start after damage to the skin.

Conditions linked with it include inflammatory bowel disease such as ulcerative colitis or Crohn's disease, rheumatoid arthritis, blood disorders such as myelodysplastic syndrome, hepatitis and Behçet's disease, according to the NHS. The dermatologists add that rarely it can be linked with underlying cancers or triggered by medications. People do not always have another condition.

It is not hereditary and is not passed from parent to child, say the dermatologists. It does not usually come back, but it can, especially if the underlying health problem is not fully controlled.

The dermatologists say treatment depends on severity and that the condition is often difficult to treat and may take time to heal. More than one treatment may need to be tried, and you remain under follow-up until it is controlled. Mild disease can be treated with creams or ointments, including corticosteroids and calcineurin inhibitors such as tacrolimus.

More severe disease is often managed with medicines taken by mouth or by injection. These include antibiotics such as tetracyclines or dapsone, steroid tablets, immunosuppressive medicines such as mycophenolate mofetil, ciclosporin or azathioprine, and biologic injections such as infliximab, adalimumab and ustekinumab, increasingly used when disease resists treatment. The dermatologists point out that stronger systemic treatments carry a higher risk of side effects, so monitoring matters.

The NHS also lists dressings and bandages to protect the ulcer and steroid injections. The two sources differ on surgery: the NHS says rarely surgery may be needed to remove ulcers, while the dermatologists say skin grafts and surgery are not usually options because they often fail and can make the ulcer bigger. Discuss any proposed operation with a dermatology team that knows pyoderma gangrenosum.

The British Association of Dermatologists places the condition in a group called neutrophilic dermatoses, in which neutrophils, a type of white blood cell, build up in an area of skin. The name sounds alarming. Pyoderma gangrenosum is not gangrene, which is caused by a loss of blood supply, and that does not happen here.

The NHS describes the main symptom as a large, painful skin ulcer. It is rare, and because it can resemble other ulcers, it is often confused with them at first. Both the NHS and the dermatologists stress that you should not try to diagnose it yourself.

It usually starts as a small bump, spot or blood blister that gets bigger quickly and turns into an ulcer, according to the NHS. There is usually a single large ulcer, though sometimes there are several. The ulcers usually appear on the legs or chest and can leak fluid. They may also appear around a cut or graze, a stoma, or surgical cuts.

The edge may look blue or purple on white skin, while on brown or black skin the skin around the ulcer may be darker than the rest. Other symptoms listed by the NHS include stiff joints, aching and painful muscles and a high temperature. After healing, a scar may form that looks different from the surrounding skin.

• A rapidly enlarging, painful ulcer, often on the legs

• A ragged purple or darker edge, depending on skin tone

• Ulcer appearing at a wound, graze or stoma site

• Fluid or pus leaking from the ulcer if it becomes infected

• Joint stiffness, muscle aches or a fever in some people

The British Association of Dermatologists says there is no single test that confirms the condition. Diagnosis is based on examining the skin, ruling out other causes of ulcers and carrying out tests for related conditions. Conditions that can look similar include venous ulcers, inflammation of blood vessels, skin infection or injury, and cancer. The NHS adds insect bites and skin tumours.

A swab may be taken to check for infection, and you may be asked for blood, urine and stool samples to look for linked conditions. A small skin biopsy can help rule out other causes of ulceration. Because treatment decisions follow, a dermatologist is usually involved early.

Healing can take a long time and scarring is possible, as the NHS notes. Keeping the wound protected, taking medicines as prescribed and attending follow-up all matter, as does managing any linked illness such as bowel inflammation. Pain control is a legitimate part of treatment, so mention it.

See a GP for any skin ulcer that is not getting better. Seek urgent medical advice if an ulcer is growing quickly, becomes red, hot, swollen or smelly, produces pus, or you feel feverish or unwell. Tell any doctor treating a leg ulcer that pyoderma gangrenosum has been diagnosed, since some standard ulcer treatments may not suit it.