pyoderma gangrenosum

Pyoderma gangrenosum is an inflammatory, non-infectious ulcerative skin condition classified among the neutrophilic dermatoses (like Sweet syndrome). Pathophysiology involves dysregulated neutrophil function and innate immune activation, though the exact mechanism remains unclear; it is thought to involve aberrant immune response, often triggered by minor trauma (pathergy). Lesions typically begin as small pustules or papules that rapidly progress to painful ulcers with a necrotic, purulent base and a characteristic violaceous, undermined border. Common sites include the lower extremities, but lesions can occur anywhere, including at surgical or trauma sites (pathergy phenomenon).

PG is frequently associated with systemic diseases: inflammatory bowel disease (both Crohn's disease and ulcerative colitis) is the most common association, followed by rheumatoid arthritis, seronegative arthritis, and hematologic disorders such as myelodysplastic syndrome, monoclonal gammopathy (IgA), and leukemia. Diagnosis is one of exclusion—infections, vasculitis, malignancy, and other causes of ulceration must be ruled out with biopsy and cultures. Histopathology typically shows dense neutrophilic infiltration but is nonspecific and mainly helps exclude other diagnoses.

Treatment involves immunosuppression: high-dose systemic corticosteroids are first-line, with steroid-sparing agents like cyclosporine, infliximab, or other biologics used for refractory or severe cases. Importantly, debridement or surgical intervention should generally be avoided due to the pathergy phenomenon, which can worsen ulceration. Management of the underlying systemic disease (e.g., IBD) is also important. Clinically, PG is a classic board question when a patient with IBD develops a rapidly enlarging, painful skin ulcer that doesn't respond to antibiotics and worsens with debridement.