What clinical features should I look for to differentiate pyoderma gangrenosum from other ulcerative skin conditions?

To differentiate pyoderma gangrenosum (PG) from other ulcerative skin conditions, look for the following clinical features:

• Rapidly progressive painful ulcers with undermined, violaceous, or bluish borders are characteristic of PG, often starting as pustules or nodules that break down quickly NICE NG12 Crowson et al. 2003.
• Pathergy phenomenon is common, where minor trauma or surgical wounds exacerbate or trigger new lesions, which is less typical in other ulcerative conditions NICE NG12 Conrad & Trüeb 2005.
• Associated systemic diseases such as inflammatory bowel disease, rheumatoid arthritis, or hematological malignancies are frequently present in PG patients, providing important diagnostic clues NICE NG12 Ashchyan et al. 2018.
• Histopathology typically shows a neutrophilic infiltrate without evidence of infection or vasculitis, helping to exclude infectious or vasculitic ulcers NICE NG12 Crowson et al. 2003.
• Exclusion of infection and malignancy is essential, as PG is a diagnosis of exclusion; ulcers do not respond to antibiotics and may worsen with surgical debridement NICE NG12 Conrad & Trüeb 2005.
• Lesion location often involves the lower extremities but can occur anywhere; the presence of multiple lesions or satellite pustules around ulcers supports PG NICE NG12 Ashchyan et al. 2018.

In summary, the key differentiating clinical features of pyoderma gangrenosum include rapidly enlarging painful ulcers with violaceous undermined borders, pathergy, association with systemic inflammatory diseases, neutrophilic histology, and exclusion of infection or malignancy NICE NG12 Crowson et al. 2003Conrad & Trüeb 2005Ashchyan et al. 2018.