Snapshot A 35-year-old man with a history of Crohn’s disease presents to his doctor with a large ulcer on his left shin. A week ago, he accidentally ran into the corner of his coffee table and hurt his left shin. Since then, a small pustule that formed at the site after the bump has progressed into a large 5 cm ulcer. On exam, the border is purple and raised. The lesion is extremely painful. Introduction Necrotizing noninfectious, inflammatory disease with painful necrotic ulcers Pathogenesis due to immune dysregulation inciting event may be due to trauma Epidemiology rare common in patients 20 - 60 year of age rare in children Associated conditions more than half of patients have inflammatory diseases inflammatory bowel disease (most common) rheumatoid arthritis seronegative spondyloarthropathies myeloproliferative diseases Presentation Symptoms pathergy (enlargening or worsening lesion) with trauma is characteristic painful lesions on lower legs, buttocks, abdomen Physical exam multiple tender red pustules that ulcerate sharply demarcated ulcer with raised, violaceous border purulent base fully evolved lesion < 10 cm in diameter lesions may coalesce into larger ulcers with crater-hole lesions Evaluation Skin biopsy not always diagnostic useful in ruling out other lesions, like vasculitis neutrophilic infiltrate Differential Infected ulcer Behçet’s disease Wegener’s granulomatosis Spider bite Treatment Treat underlying condition For superficial lesions topical corticosteroids, tacrolimus, or cyclosporine For deep/large lesions systemic steroids systemic cyclosporine Prognosis, Prevention, and Complications Prognosis chronic, relapsing ulcers leave atrophic scars when healed