DermNet NZ

Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Pyoderma gangrenosum

What is pyoderma gangrenosum?

Pyoderma gangrenosum presents as a rapidly enlarging, very painful ulcer. It is one of a group of autoinflammatory disorders known as neutrophilic dermatoses.

The name pyoderma gangrenosum is historical. The condition is not an infection (pyoderma), nor does it cause gangrene.

Who gets pyoderma gangrenosum?

Pyoderma gangrenosum is an uncommon disease that affects males and females of any age, but is more common in those aged over 50 years. It is thought to be a reaction to an internal disease or condition. Known associations include:

However, about 50% of those affected by pyoderma gangrenosum have none of the associated risk factors.

Clinical features of pyoderma gangrenosum

Pyoderma gangrenosum usually starts quite suddenly, often at the site of a minor injury. It may start as a small pustule, red bump or blood-blister. The skin then breaks down resulting in an ulcer. The ulcer can deepen and widen rapidly. Characteristically, the edge of the ulcer is purple and undermined. Pyoderma gangrenosum is usually very painful. Several ulcers may develop at the same time.

Untreated, the ulcers may continue to enlarge, persist unchanged or may slowly heal. Treatment is usually successful in arresting the process, but complete healing may take months. This is particularly true if there is underlying venous disease, another reason for leg ulcers.

Deep ulcers heal with scarring and this is sometimes with a characteristic cribriform or criss-cross pattern. A rare superficial bullous variant of pyoderma gangrenosum may heal without leaving a scar. This may be similar to or confused with acute febrile neutrophilic dermatosis (Sweet disease).

Pyoderma gangrenosum Pyoderma gangrenosum Pyoderma gangrenosum
Pyoderma gangrenosum Pyoderma gangrenosum Pyoderma gangrenosum
Pyoderma gangrenosum

How is pyoderma gangrenosum diagnosed?

Pyoderma gangrenosum is diagnosed by its characteristic appearance. There is no specific test. The wound should be swabbed and cultured for micro-organisms, but these are not the cause of pyoderma gangrenosum. Biopsy may be necessary to rule out other causes of ulceration. Pyoderma gangrenosum characteristically results in a neutrophilic inflammatory infiltrate but this is not always present.

Mostly, blood tests are not particularly helpful. Some patients may have a positive ANCA (antineutrophil cytoplasmic antibody).

The pathergy test is usually positive (a skin prick test causing a papule, pustule or ulcer).

Treatment of pyoderma gangrenosum

Treatment is non-surgical. The necrotic tissue should be gently removed. Wide surgical debridement should be avoided during the active stage of pyoderma gangrenosum because it may result in enlargement of the ulcer.

Often conventional antibiotics such as flucloxacillin are prescribed prior to making the correct diagnosis. These may be continued if bacteria are cultured in the wound (secondary infection) or there is surrounding cellulitis (red hot painful skin), but they are not helpful for uncomplicated pyoderma gangrenosum.

Small ulcers are best treated with:

Systemic treatment for larger ulcers due to pyoderma gangrenosum may include:

Outlook or prognosis for pyoderma gangrenosum is unpredictable.

Related information

On DermNet NZ:

Other websites:

Books about skin diseases:

See the DermNet NZ bookstore

Author: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, 1998. Updated September 2015.

DermNet NZ does not provide an online consultation service.
If you have any concerns with your skin or its treatment, see a dermatologist for advice.