Introduction

Pyoderma gangrenosum is a rare, inflammatory skin condition characterised by painful, necrotic ulcers. Despite its name, the condition is not caused by infection or gangrene. Instead, it is often associated with systemic diseases, including autoimmune disorders, inflammatory bowel disease, and haematological malignancies. Pyoderma gangrenosum belongs to a group of disorders called neutrophilic dermatoses and can vary widely in its presentation. There are four primary clinical variants: classic ulcerative, pustular, bullous (vesicular-bullous), and vegetative (superficial granulomatous) forms. This article explores each type in detail and discusses diagnosis and treatment.^1,2

Overview of pyoderma gangrenosum

Pyoderma gangrenosum affects adults more commonly than children, although paediatric cases have been reported, representing less than 5% of all cases. The disease can occur across a wide age range, from early adolescence to older adulthood.¹

It often develops in individuals with underlying systemic conditions such as rheumatoid arthritis, inflammatory bowel disease, or other autoimmune disorders. In some cases, it is associated with solid tumours or haematological malignancies. Pyoderma gangrenosum is characterised by an abnormal immune response, leading to neutrophil infiltration and tissue damage.¹

Types of pyoderma gangrenosum

Classic ulcerative pyoderma gangrenosum

This is the most common and severe form of pyoderma gangrenosum. It typically affects the pre-tibial area but can appear on any part of the body, including the trunk, head and neck, upper limbs, and genital regions. Lesions often present at multiple sites simultaneously.

• Ulcers generally start as small pustules or papules, often follicular in origin, and rapidly expand into deep, painful ulcers
• The lesions have well-defined, raised, and undermined edges with a violaceous to bluish colour
• Surrounding skin may appear red and firm (erythema and induration), clearly separating the lesion from unaffected tissue
• The ulcer base may involve deeper layers, including subcutaneous tissue and muscle, often containing granulation tissue, purulent discharge, and blood
• Healing occurs via re-epithelialisation from the edges, frequently resulting in cribriform (net-like) scarring. Scarring can be cosmetically significant if treatment is delayed^1,2

Vesicular-Bullous Pyoderma Gangrenosum

This superficial variant usually affects the upper limbs and face and is commonly linked with haematological malignancies.

• Lesions begin as bullae (fluid-filled blisters) that enlarge concentrically, eventually forming superficial erosions or ulcers
• Bullous pyoderma gangrenosum resembles Sweet Syndrome, another neutrophilic dermatosis
• This variant is often accompanied by systemic symptoms such as fever and joint pain
• Prognosis is generally poorer when associated with leukaemia compared to other variants^1,2

Pustular pyoderma gangrenosum

This superficial form is frequently associated with inflammatory bowel disease.

• Lesions present as small pustules on normal-appearing skin
• Pustules may persist for months without progressing but can sometimes evolve into ulcers, resembling the ulcerative variant.
• Disease activity often correlates with underlying bowel disease, and treatment of the systemic condition may improve skin symptoms
• Pyostomatitis vegetans, a pustular condition of the oral mucosa, can co-occur in up to 50% of cases^1,2

Vegetative (Superficial Granulomatous) Pyoderma Gangrenosum

Vegetative pyoderma gangrenosum is milder and progresses slowly.

• Lesions are usually solitary and lack the violaceous undermined edges and purulent base seen in ulcerative pyoderma gangrenosum
• It responds well to less intensive treatments and often occurs in otherwise healthy individuals
• Though rare, vegetative pyoderma gangrenosum has been linked to Behçet’s disease, rheumatoid arthritis, diabetes mellitus, and haematological disorders^1,2

Diagnosis

Diagnosis of pyoderma gangrenosum is mainly one of exclusion, as there are no definitive laboratory markers. Clinicians consider the condition in patients with chronic, non-healing ulcers, particularly when associated with systemic diseases.¹

Histology is generally non-specific but often shows a sterile neutrophilic infiltrate in the dermis, occasionally with mixed inflammatory cells or lymphocytic vasculitis. In 2004, diagnostic criteria were proposed, requiring:

Major criteria

• Rapid development of a painful necrotic ulcer with irregular, undermined borders
• Exclusion of other causes of ulceration

Minor criteria

• History of pathergy (lesion development after minor trauma) or cribriform scarring
• Association with systemic conditions such as inflammatory bowel disease, arthritis, or haematological disease
• Histopathological findings consistent with sterile neutrophilic infiltrate
• Rapid response to systemic corticosteroids

Differential diagnosis

A careful assessment is needed to rule out:

• Infectious ulcers: Mycobacterial or deep fungal infections
• Drug-induced dermatoses: Iododerma, Bromoderma
• Vascular ulcers: Arterial ulcers, Martorell ulcers

Treatment

Management is tailored to disease severity and underlying conditions.

• Treating associated systemic diseases is essential, though skin severity does not always correlate with systemic disease activity
• Rapidly progressive ulcers may require systemic immunosuppressants such as oral corticosteroids or cyclosporine
• Avoid unnecessary surgery due to pathergy risk
• Milder cases can be managed with topical or intralesional corticosteroids, topical tacrolimus, nicotine, dapsone, or sodium cromoglycate
• Wound care is critical, including gentle cleaning and conservative debridement to remove nonviable tissue while avoiding trauma
• Biologic therapies, including anti-TNF agents, IL-12/23 inhibitors, IL-1 beta inhibitors, and IL-6 inhibitors, have shown efficacy in refractory cases

FAQs

What causes pyoderma gangrenosum?

Pyoderma gangrenosum is not caused by infection or gangrene. It is an inflammatory condition often linked to underlying systemic diseases, such as inflammatory bowel disease, rheumatoid arthritis, diabetes, or blood disorders. The exact trigger is not fully understood, but the immune system plays a key role in damaging the skin.

How is pyoderma gangrenosum diagnosed?

Diagnosis is mainly made by ruling out other causes of chronic, non-healing ulcers. Doctors rely on the appearance of the ulcers, patient history, underlying conditions, and response to treatment. Skin biopsies and lab tests may help, but there is no single definitive test.

Can pyoderma gangrenosum be cured?

There is no permanent cure, but the condition can be managed effectively. Treatment depends on severity and may include topical or systemic medications, wound care, and addressing underlying diseases. Biologic therapies can help in cases that do not respond to standard treatments.

What is pathergy, and why is it important in pyoderma gangrenosum?

Pathergy is a reaction where new ulcers form at sites of minor trauma, such as scratches, injections, or surgical wounds. It is important because even minor injury can worsen pyoderma gangrenosum, so surgical procedures and aggressive debridement are usually avoided.

Are all types of pyoderma gangrenosum equally severe?

No. The ulcerative type is the most aggressive, causing deep, painful ulcers. Bullous pyoderma gangrenosum is often associated with blood cancers and can be serious. Pustular and vegetative forms are usually milder, with slower progression and less tissue destruction.

Summary

Pyoderma gangrenosum is a severe, inflammatory skin disorder that can cause painful ulcers, scarring, and systemic symptoms. Early diagnosis and treatment are essential to prevent complications. The ulcerative variant is most aggressive, while bullous, pustular, and vegetative forms have distinct presentations and associations. Diagnosis relies on clinical evaluation, exclusion of mimics, and response to treatment. Management combines systemic and local therapies, wound care, and attention to underlying disease, with biologic agents offering promising results for refractory cases. With early recognition and comprehensive care, patients can achieve significant improvement and symptom control.