What is Pyoderma Gangrenosum?
Pyoderma gangrenosum (PG) is a rare, painful neutrophilic dermatosis characterized by rapidly developing necrotic skin ulcerations with undermined borders, purulent material that is sterile on culture, and a strong association with systemic inflammatory diseases, particularly inflammatory bowel disease. 1
Clinical Presentation
Lesion Characteristics:
- Initially presents as single or multiple erythematous papules or pustules that rapidly progress to deep excavating ulcerations 1
- The ulcers contain purulent material that is sterile on culture unless secondary wound infection has occurred 1
- Hallmarked by undermined, irregular, erythematous-violaceous borders with peripheral erythema 2, 3
- Lesions are preceded by trauma at the site in 20-30% of cases through a phenomenon called pathergy 1, 4
Common Locations:
- Most frequently affects the lower extremities, particularly the shins 1, 5
- Can occur anywhere on the body including genitalia 1
- Adjacent to stomas (peristomal PG) 1
Epidemiology and Associated Conditions
Demographics:
- Average age of onset is in the mid-40s, affecting the third to sixth decades of life 5, 3
- Incidence of a few cases per million person-years 3
- Affects men and women almost equally 5
Systemic Disease Associations:
- 50-70% of cases are associated with underlying systemic disorders 4
- Occurs in 0.6-2.1% of ulcerative colitis patients, with higher frequency than in Crohn's disease 1, 4
- Commonly associated with inflammatory bowel disease, hematological malignancies, and rheumatologic disorders 4
- PG may precede the diagnosis of the underlying condition, particularly IBD 4
Pathophysiology
Immune Dysregulation:
- Considered an autoinflammatory disorder within the spectrum of neutrophilic dermatoses 1, 6, 3
- Involves profound dysregulation of both innate and adaptive immunity 2
- T helper 17/T helper 1-skewed inflammation with exaggerated inflammasome activation 2
- Dysregulated neutrophil-dominant milieu with elevated levels of TNF-α, IL-1β, IL-8, IL-17, IL-23, and IL-36 2
- Abnormal neutrophil function and impaired cellular immunity play key roles 4
Diagnosis
Diagnostic Approach:
- PG is a diagnosis of exclusion with no specific laboratory or histopathologic findings to confirm diagnosis 5
- Biopsy from the periphery of the lesion is recommended to help exclude other disorders, though findings are non-specific 7, 4
- Histology reveals non-caseating granulomas in some cases and demonstrates a perivascular and diffuse infiltrate of neutrophils 1
Critical Differential Diagnoses:
- Ecthyma gangrenosum (bacterial cutaneous vasculitis requiring antibiotics, not immunosuppression) presents as painless erythematous papules progressing to painful necrotic lesions within 24 hours, whereas PG is a sterile inflammatory process 7
- Infection, vascular insufficiency ulcers, systemic vasculitides, autoimmune disease, and malignancy 5
- Metastatic Crohn's disease, which may appear as nodules, plaques, or ulcers with non-caseating granulomas on histology 1
Clinical Spectrum
Related Neutrophilic Dermatoses:
- PG forms part of the spectrum of neutrophilic dermatoses associated with IBD, which includes Sweet's syndrome, pustular eruption of ulcerative colitis, and bowel-associated dermatosis-arthritis syndrome 1
- Sweet's syndrome is characterized by tender, red inflammatory nodules or papules, usually affecting upper limbs, face, or neck, with strong predilection for women and patients with colonic involvement 1
Common Pitfalls
Misdiagnosis Risk:
- Misdiagnosis occurs in a substantial percentage of cases 7
- The disease is frequently misdiagnosed and often requires work-up for underlying systemic disease 5
Surgical Intervention:
- Avoid surgical debridement during active disease due to pathergy, as trauma can trigger new lesion development 7
- Surgical intervention should be reserved for after disease control or for progressive necrotizing fasciitis 7
Recurrence: