Pyoderma Gangrenosum

What pyoderma gangrenosum is

PG belongs to a group called neutrophilic dermatoses, in which neutrophils, a type of white blood cell, flood into the skin and destroy tissue without any infection. The exact trigger is not known, but it involves faulty regulation of the innate immune system.

It is rare, affecting a few people per million each year, usually adults between 20 and 50, and slightly more women than men. Children are rarely affected.

Symptoms

PG usually starts as:

• a small red or purple bump, blister or pustule, sometimes resembling an insect bite or a spot
• intense pain, often more than its size suggests

Within days, it breaks down into an ulcer that:

• enlarges quickly, sometimes by centimeters in a week
• has a purple or gray, raised edge that is undermined (the ulcer extends under the border)
• has a moist, sometimes pus-covered or bleeding base
• may join with other ulcers

The lower legs are the most common site. PG can also occur around stomas, at surgical wounds, on the trunk, face, hands and, rarely, in the mouth, eyes or internal organs. People may feel unwell, with fever and joint aches.

Pathergy

About a quarter to a third of people experience pathergy: new ulcers or worsening after minor skin injury, such as a needle prick, a bump, a biopsy or surgery. This is why surgical cleaning (debridement) of a PG ulcer often makes it larger.

Types

Causes and associated diseases

About half of people with PG have an underlying condition:

• Inflammatory bowel disease: Crohn's disease and ulcerative colitis. PG may flare with bowel disease or occur independently.
• Inflammatory arthritis: rheumatoid arthritis and other forms.
• Blood disorders: monoclonal gammopathy, myelodysplastic syndrome, leukemia and myeloma.
• Other: hidradenitis suppurativa, autoinflammatory syndromes (such as PAPA syndrome) and some medicines.

Your doctor will look for these conditions, because treating them can help control PG.

Diagnosis

There is no single test for PG. It is diagnosed by recognizing the typical pattern and excluding conditions that look similar. Tests include:

• Skin biopsy from the edge of the ulcer, to show neutrophil infiltration and exclude vasculitis, cancer and specific infections. Biopsy can cause pathergy, so it is done carefully.
• Swabs and tissue cultures for bacteria, fungi and mycobacteria.
• Blood tests: blood count, inflammation markers, kidney and liver function, protein electrophoresis for monoclonal proteins, and autoantibodies.
• Colonoscopy if bowel symptoms suggest IBD.

Conditions it can be confused with include infected wounds, necrotizing fasciitis, venous or arterial leg ulcers, spider bites, vasculitis and skin cancer. PG is often first treated as infection without improvement.

Treatment

Treatment aims to stop inflammation, relieve pain and help the ulcer heal. A dermatologist leads care, often with gastroenterology, rheumatology or hematology.

Wound care

• moist, non-stick dressings
• gentle cleaning without aggressive scrubbing
• compression for leg ulcers when circulation is adequate and the doctor agrees
• avoiding surgical debridement during active disease
• treating any secondary infection

Pain relief

PG is very painful. Regular pain relief, including acetaminophen (paracetamol) and stronger prescription medicines where needed, is part of treatment.

Local treatments

For small or early lesions: strong topical corticosteroids, topical tacrolimus, or steroid injections into the ulcer edge.

Systemic treatments

• Oral corticosteroids such as prednisone, often the first systemic treatment for rapid control
• Cyclosporine, which has been shown to be about as effective as prednisone in a trial
• Biologic medicines: infliximab has the strongest evidence among biologics. Adalimumab, ustekinumab and others are used, especially with IBD
• Other options: dapsone, mycophenolate, methotrexate, intravenous immunoglobulin, and newer agents in trials

Treatment often continues for months. Steroids are tapered once ulcers are healing.

Surgery

Surgery is avoided while PG is active. Skin grafts may be considered once inflammation is controlled, under immune-suppressing treatment. For people with a history of PG, planned surgery should be discussed with the dermatologist, who may adjust treatment around the operation.

Outlook

With treatment, most ulcers heal over months, leaving thin, wrinkled scars that look like tissue paper or a sieve (cribriform scars). Recurrence is common, especially if the underlying disease flares. Untreated PG can cause large ulcers, infection and significant disability.

Frequently asked questions

What does pyoderma gangrenosum look like?

It usually begins as a painful red bump or pustule that quickly breaks down into an ulcer. The ulcer has a purple or gray edge that overhangs the wound and a wet, sometimes pus-covered base. It grows over days and is far more painful than an ordinary wound of the same size.

Is pyoderma gangrenosum an infection?

No. Despite its name, which comes from older theories, it is not caused by bacteria and is not gangrene. It is an inflammatory reaction driven by the immune system. Ulcers can become secondarily infected, but antibiotics alone do not heal PG.

What is the link between pyoderma gangrenosum and IBD?

Pyoderma gangrenosum is one of the skin conditions associated with Crohn's disease and ulcerative colitis. It may appear during bowel flares or independently. Treating the IBD, often with biologics such as infliximab, can also help control PG.

Why should pyoderma gangrenosum not be debrided?

Many people with PG have pathergy, meaning skin injury triggers more inflammation. Cutting away tissue, as is done for infected wounds, often makes the ulcer larger and deeper. Gentle wound care combined with immune-suppressing medicine is the safer approach.

Can pyoderma gangrenosum be cured?

Individual ulcers usually heal with treatment, but PG can come back, especially if an associated disease flares. Some people have a single episode; others need long-term treatment. Controlling any underlying condition and protecting the skin from injury lower the risk of recurrence.