Pyoderma gangrenosum is a rare skin reaction to a disease or illness, which results in painful skin ulcers. It is treatable with medication, but may take some time to heal. 

It usually suddenly starts as a small pimple, red bump or blood blister. The skin then breaks down to a painful ulcer, which may ooze fluid.

The ulcer can rapidly get bigger and deeper, and several may develop in the area. If they get infected you may feel unwell and develop a fever.

Pyoderma gangrenosum usually affects the legs, although it can effect any area of skin, including around the head and neck, upper limbs and genitals. Occasionally, it develops around the site of an injury or surgical wound, such as a stoma (see what causes it? below). 

Despite the similar-sounding name, pyoderma gangrenosum is not related to gangrene.

Who is affected?

Pyoderma gangrenosum is seen in men and women of any age, but usually affects young and middle-aged adults.

People with the following health conditions are particularly susceptible:

• ulcerative colitis or Crohn’s disease (diseases that cause persistent inflammation of the bowel) 
• rheumatoid arthritis 
• blood dyscrasia, a blood disorder
• hepatitis (inflammation of the liver) 
• granulomatosis with polyangiitis, an uncommon disorder in which the walls of blood vessels become inflamed and leaky
• PAPA syndrome, a rare genetic disorder 

What causes it? 

Pyoderma gangrenosum is thought to be a skin reaction to a disease or illness, such as the health conditions listed above. 

However, about half of all people with pyoderma gangrenosum have none of these conditions and there are no known reasons for it.

There is a high concentration of neutrophils (white blood cells involved in inflammation) in the affected tissue, which suggests an overactive immune system. 

Sometimes, the reaction may be triggered by minor skin damage or an injury – for example, it may develop around the site of a stoma or surgical wound, a needle prick, a biopsy or an insect bite. 

The skin reaction is not hereditary (inherited), so it’s not passed from parents to their children. It is not contagious either, so it cannot be transferred from or to another person.

How is it diagnosed?

There is no specific blood test for pyoderma gangrenosum.

If your doctor suspects you have the skin reaction, they may take a sample of your skin (a biopsy) to examine under the microscope in a laboratory. This helps rule out other causes of skin ulcers.

Your doctor may take a swab of the wound to rule out infection, and may order blood tests to check for conditions that may be associated with pyoderma gangrenosum.

How is it treated?

Pyoderma gangrenosum is treatable, but may take some time to heal. 

Care of the wound

The dead tissue should be gently removed, and dressings may be needed to soak up any discharge and help retain the creams applied to the wound.

Steroid creams, ointments or injections

Strong steroid creams or ointments are applied on and around ulcers daily or on alternate days. They often help the ulcers heal quickly, particularly if they are small and diagnosed early.

Alternatively, the steroid medication triamcinolone may be injected into the edge of the ulcer. This may be tried on its own or along with steroid tablets.

Tacrolimus ointment has proved useful in treating ulcers, but infection is a possible complication with this treatment.

Steroid tablets

Steroid tablets such as prednisolone are usually the first drug treatment to try, either on their own or with minocycline (an antibiotic). This generally reduces the inflammation.

However, the long-term use of steroids is associated with bone thinning (osteoporosis), so they need to be used with caution. 

Read about the side effects of prednisolone.

Immunosuppressants

Pyoderma gangrenosum is caused by an overactive immune system, and immunosuppressants (drugs that suppress the immune system) have proved useful in healing the ulcers. They help reduce the pain and swelling.

A few examples are ciclosporin, mycophenolate mofetil, and newer treatments such as infliximab, which are used for more severe cases of the condition.

However, immunosupressants can have unpleasant side effects and will need specialist supervision for their administration, as well as monitoring. They are not currently licensed for the treatment of pyoderma gangrenosum.

What’s the outlook?

In many people with pyoderma gangrenosum, the ulcers heal with relatively simple treatments.

However, the progression of the disease varies from person to person – it may suddenly clear up, stay the same for months or years, or slowly heal over many months. Treatment usually stops it getting worse.

Some people have flare-ups after the slightest injury or for no apparent reason, and it may recur.

Possible complications include scarring of the skin tissue and infection.