From the Guidelines
Diagnosing Pyoderma gangrenosum (PG) is primarily a clinical process that involves excluding other conditions through a process of elimination, based on the characteristic appearance of the lesions and the exclusion of other possible skin diseases. The diagnosis of PG can be challenging, as it is a diagnosis of exclusion, and can be misdiagnosed in a substantial percentage of cases 1. PG typically presents as single or multiple erythematous papules or pustules that quickly become deep excavating ulcerations with purulent material that is sterile on culture, unless secondary wound infection has occurred 1.
Some key characteristics of PG include:
- The appearance of a skin pustule that quickly becomes a burrowing ulcer with violaceous edges
- A size between 2 cm and 20 cm in diameter
- The potential to expose tendons, muscles, and deep tissues
- The commonest sites are the shins and adjacent to stomas, but it can occur anywhere on the body, including the genitalia 1
In some cases, a biopsy from the periphery of the lesion can help, as findings in PG are non-specific, but biopsy can be helpful to exclude other skin disorders 1. A detailed medical history is essential, focusing on associated conditions like inflammatory bowel disease, as PG is often associated with these disorders. Laboratory tests and cultures of the wound should be performed to assess for underlying systemic diseases, inflammation, and infectious causes. Ultimately, the diagnosis of PG relies on the clinician's ability to recognize the characteristic clinical presentation and exclude other causes of similar-appearing ulcers.
From the Research
Diagnostic Criteria for Pyoderma Gangrenosum
The diagnosis of Pyoderma gangrenosum (PG) is challenging due to the lack of definitive laboratory or histopathological criteria 2, 3. However, several studies have proposed diagnostic criteria to aid in the diagnosis of PG. A Delphi consensus exercise yielded one major criterion and eight minor criteria for the diagnosis of ulcerative PG 4. The major criterion is a biopsy of the ulcer edge demonstrating a neutrophilic infiltrate, while the minor criteria include:
- Exclusion of infection
- Pathergy
- History of inflammatory bowel disease or inflammatory arthritis
- History of papule, pustule, or vesicle ulcerating within 4 days of appearing
- Peripheral erythema, undermining border, and tenderness at ulceration site
- Multiple ulcerations, at least one on an anterior lower leg
- Cribriform or "wrinkled paper" scar(s) at healed ulcer sites
- Decreased ulcer size within 1 month of initiating immunosuppressive medication(s)
Diagnostic Work-up for Pyoderma Gangrenosum
A retrospective analysis of US insurance claims-based data found that only a minority of patients with PG underwent skin biopsy and/or tissue culture prior to diagnosis 5. The study found that:
- 9.4% of patients underwent skin biopsy
- 8% underwent tissue culture
- 1.4% underwent both skin biopsy and tissue culture This suggests that patients may receive a diagnosis of PG without having tissue evaluation, which can increase the risk of misdiagnosis and misdirected treatment.
Clinical Presentation of Pyoderma Gangrenosum
PG typically presents as a painful, rapidly evolving cutaneous ulcer with undermined, irregular, erythematous-violaceous edges 2, 3, 6. The lower legs are most frequently affected, although PG can present at any body site. Other subtypes of PG include bullous, vegetative, pustular, peristomal, and superficial granulomatous variants 2.
Laboratory Tests and Histopathology
Laboratory tests of biopsied wound tissue are required for an accurate diagnosis of PG 3. Histologic evaluation and exclusion of other entities are central to the diagnosis of PG 5. A biopsy of the ulcer edge demonstrating a neutrophilic infiltrate is a major criterion for the diagnosis of ulcerative PG 4.