Pyoderma gangrenosum is a rare and painful skin condition that causes open, ulcerating wounds on the skin. Despite its name, it is neither an infection nor related to gangrene, but rather an inflammatory disorder of the immune system that can develop suddenly and progress rapidly.

Epidemiology

Pyoderma gangrenosum is an uncommon condition that affects only a small portion of the population worldwide. The estimated incidence ranges from approximately 3 to 10 cases per million people each year, though some sources suggest around 6 cases per million annually.^[1][2][3] This rarity means that many healthcare professionals may encounter very few cases during their careers, which can sometimes lead to challenges in recognition and diagnosis.

The condition can affect people of any age, including infants and elderly individuals, though it shows particular demographic patterns. The peak incidence occurs most commonly between the ages of 20 and 50 years, though some research indicates that most patients are 55 years of age or older.^[1][2] Cases in children and adolescents are notably rare, accounting for only about 4 percent of all pyoderma gangrenosum diagnoses.^[3]

Women appear to be affected more frequently than men, though pyoderma gangrenosum can develop in either sex.^[1][2] The gender difference is particularly notable in middle-aged adults, where the condition is observed more often in females. The reasons for this gender disparity are not fully understood, but may relate to differences in immune function or the prevalence of associated underlying conditions.

Causes

The exact cause of pyoderma gangrenosum remains unknown, which makes it a challenging condition to understand and prevent. Medical experts believe it to be a disorder of the immune system, specifically an autoinflammatory disease, which means the body’s immune system mistakenly attacks healthy tissue in the skin.^[1][2] This is different from a typical infection, as the name might suggest.

The condition involves problems with certain white blood cells called neutrophils, which are part of the body’s natural defense system against infections. In pyoderma gangrenosum, these neutrophils react excessively and infiltrate the skin tissue, causing inflammation and tissue breakdown.^[3][4] The pathophysiology is poorly understood but may involve problems with neutrophil movement and function. A substance called interleukin-8, which is involved in inflammation, is found in excessive amounts in the affected skin areas.^[5]

Pyoderma gangrenosum is not contagious and cannot be transmitted from one person to another through physical contact or any other means.^[1][2] It is also not caused by poor hygiene or lifestyle choices. Some evidence suggests there may be a genetic component, meaning that certain people may inherit a predisposition to developing the condition, though this is not fully established.^[4]

Certain medications have occasionally been implicated as triggers for pyoderma gangrenosum. These include cocaine (particularly when adulterated with levamisole), isotretinoin (used for severe acne), propylthiouracil (for thyroid conditions), and sunitinib (a protein kinase inhibitor used in cancer treatment).^[4][5] However, drug-induced cases remain relatively uncommon.

Risk Factors

While approximately half of people who develop pyoderma gangrenosum have no identifiable underlying condition, the other half have associated systemic diseases. Understanding these risk factors is important because the presence of certain conditions significantly increases the likelihood of developing pyoderma gangrenosum.^[1][2]

Inflammatory bowel disease is one of the most common associations. People with ulcerative colitis or Crohn’s disease have a notably higher risk of developing pyoderma gangrenosum. In fact, pyoderma gangrenosum represents the second most common skin manifestation in patients with inflammatory bowel disease, affecting between 1 and 3 percent of these individuals.^[4] It is more commonly seen as a complication of ulcerative colitis compared to Crohn’s disease. Interestingly, the underlying bowel disease is often active in more than half of patients at the time pyoderma gangrenosum appears.

Rheumatoid arthritis and other inflammatory joint conditions also increase the risk of pyoderma gangrenosum. People with these autoimmune forms of arthritis have overactive immune systems that may predispose them to other inflammatory conditions affecting the skin.^[1][2]

Blood disorders represent another important risk category. These include conditions such as myelodysplastic syndrome, various forms of leukemia, lymphoma, and monoclonal gammopathy (an abnormal protein in the blood, usually immunoglobulin A).^[2][4] People with these blood-related conditions may develop a variant of pyoderma gangrenosum that appears as blisters rather than the typical ulcers.

Other associated conditions include chronic active hepatitis (liver inflammation), Behçet’s disease (an inflammatory condition affecting blood vessels), and granulomatosis with polyangiitis (a rare disease causing inflammation of blood vessels).^[2][4] Some rare genetic syndromes, such as PAPA syndrome, are also linked to pyoderma gangrenosum.

Symptoms

Pyoderma gangrenosum typically begins suddenly, often appearing at a site of minor injury to the skin, though it can also develop spontaneously without any obvious trigger. The initial presentation is often deceptive, as it may look like a common skin problem such as an insect bite, pimple, small red bump, or blood blister.^[1][2] This innocuous appearance often leads to misdiagnosis in the early stages.

What distinguishes pyoderma gangrenosum is the rapidity with which the condition progresses. Within days, the initial bump or blister breaks down, and the skin begins to deteriorate. The lesion transforms into an open sore or ulcer that can deepen and widen at an alarming rate.^[1][2] Some ulcers can expand significantly within a matter of days or weeks.

The appearance of a fully developed pyoderma gangrenosum ulcer is quite characteristic. The edge of the ulcer typically has a distinctive purple or blue color on light skin, while on darker skin tones, the border may appear darker than the surrounding tissue.^[2] The borders are described as “undermined,” meaning the skin at the edge overhangs the ulcer base, creating a characteristic lip or ledge.^[4] The center of the ulcer often contains necrotic (dead) tissue and may produce purulent (pus-like) or bloody discharge that can leak fluid.

Pain is a hallmark feature of pyoderma gangrenosum and is often described as severe and out of proportion to the size of the visible wound. Even small lesions can cause intense, burning pain that significantly impacts quality of life.^[1][5] The pain can be so debilitating that it interferes with sleep, mobility, and daily activities. This severe pain distinguishes pyoderma gangrenosum from many other types of skin ulcers, which may be less painful.

The most common location for pyoderma gangrenosum is the legs, particularly the lower legs and shins. However, the condition can occur anywhere on the body, including the arms, trunk (chest and abdomen), buttocks, face, and around surgical sites.^[1][2] In people with inflammatory bowel disease who have ostomies (surgical openings for waste elimination), pyoderma gangrenosum sometimes develops around the stoma site, a variant called peristomal pyoderma gangrenosum.

Patients may develop a single ulcer or multiple lesions, either appearing simultaneously or developing over time. In some cases, multiple ulcers can merge together to form larger, more complex wounds. Beyond the visible skin changes, people with pyoderma gangrenosum may experience systemic symptoms including fever, general malaise (feeling unwell), stiff joints, and muscle aches.^[2][5]

Without treatment, the natural course of pyoderma gangrenosum is unpredictable. Some ulcers may continue to enlarge, others may remain stable, and some may slowly heal on their own. However, even with successful treatment, healing can take many weeks or months, and deep ulcers typically leave significant scarring.^[4] The scars may have a characteristic cribriform or criss-cross pattern, or may appear thin, wrinkled, and darker or lighter than the surrounding skin.

Prevention

Because the exact cause of pyoderma gangrenosum is not known, there are no specific measures that can completely prevent the condition from occurring. However, for people who have been diagnosed with pyoderma gangrenosum or who have risk factors, certain strategies may help reduce the likelihood of developing new lesions or experiencing flare-ups.

The most important preventive measure is avoiding trauma to the skin. Given that pyoderma gangrenosum demonstrates pathergy (the tendency for skin injury to trigger new lesions), protecting the skin from cuts, scrapes, punctures, and other injuries is crucial.^[4][5] People with a history of pyoderma gangrenosum should take extra care during activities that might cause skin injury and should inform their healthcare providers about their condition before any planned surgical procedures.

For individuals with underlying conditions associated with pyoderma gangrenosum, effective management of those conditions may help reduce risk. People with inflammatory bowel disease, for example, should work closely with their gastroenterologists to keep their condition under good control. Similarly, those with rheumatoid arthritis or other inflammatory conditions should maintain appropriate treatment regimens as prescribed by their rheumatologists.^[1]

Early recognition and prompt treatment of pyoderma gangrenosum when it does develop is critical. People who have had the condition before should be alert to early warning signs, such as new painful bumps or rapidly progressing skin lesions, and should seek medical attention quickly. Early intervention can help prevent larger, more destructive ulcers from forming.

Maintaining overall skin health through good hygiene, adequate nutrition, and avoiding known triggers (such as certain medications that have been associated with pyoderma gangrenosum) may also be beneficial. However, it’s important to understand that pyoderma gangrenosum can occur despite these precautions, as it is fundamentally related to immune system dysfunction rather than external factors.

Pathophysiology

The pathophysiology of pyoderma gangrenosum involves complex changes in how the body’s immune system functions, particularly regarding inflammatory processes in the skin. While medical science has made progress in understanding this condition, many aspects remain unclear, which contributes to the challenges in both diagnosis and treatment.

At its core, pyoderma gangrenosum is classified as a neutrophilic dermatosis, which is a group of conditions characterized by the accumulation of neutrophils in the skin without an infectious cause.^[3][4] Neutrophils are white blood cells that normally help the body fight infections by moving to sites of injury or infection and releasing enzymes that destroy pathogens. In pyoderma gangrenosum, however, these cells accumulate in the skin inappropriately and cause tissue damage rather than protection.

The dysfunction appears to involve problems with neutrophil chemotaxis, which is the process by which these cells navigate through tissues. The neutrophils essentially become overactive and destructive.^[5] When examined under a microscope, affected skin tissue shows an abundance of neutrophils infiltrating the dermis (the deep layer of skin) and subcutaneous tissue (the layer beneath the skin), along with evidence of tissue destruction and inflammation.

Inflammatory signaling molecules called cytokines play a significant role in the disease process. Interleukin-8, a cytokine that attracts neutrophils to areas of inflammation, is found in excessive amounts in pyoderma gangrenosum lesions.^[5] Other cytokines, including tumor necrosis factor-alpha (TNF-α) and various interleukins, are also involved in promoting the inflammatory cascade that leads to tissue breakdown.

T lymphocytes, another type of immune cell, also contribute to the pathophysiology. These cells help regulate immune responses and their dysregulation may contribute to the chronic inflammation seen in pyoderma gangrenosum.^[4] The interplay between neutrophils, T cells, cytokines, and other immune system components creates a self-perpetuating cycle of inflammation and tissue destruction.

The mechanical changes that occur in the skin include progressive necrosis (death of skin tissue) that begins at the superficial layers and can extend deep into the dermis and even into underlying muscle or other structures. Blood vessels in the affected area may show inflammation, though pyoderma gangrenosum is not primarily a vasculitic condition (a disease of blood vessel inflammation). The undermined borders characteristic of the ulcers develop as inflammation and tissue destruction extend laterally beneath apparently normal-appearing skin at the edge of the lesion.

As the ulcer develops, the base becomes covered with necrotic tissue and inflammatory exudate (fluid containing dead cells, proteins, and inflammatory debris). The surrounding skin shows erythema (redness) and edema (swelling) due to the inflammatory process. The intense pain associated with pyoderma gangrenosum likely results from both the tissue destruction itself and the release of inflammatory mediators that stimulate pain receptors in the skin.