Ulcerative Colitis-Associated Vasculopathy Mimicking Antineutrophil Cytoplasmic Antibody (ANCA)-Associated Vasculitis.

Ulcerative colitis (UC) is a chronic inflammatory condition with recognized extraintestinal manifestations, including a prothrombotic state that can result in both venous and arterial complications. While venous thromboembolism is more common, arterial and microvascular thrombosis leading to digital ischemia and gangrene are rare but severe manifestations. The presence of antineutrophil cytoplasmic antibodies (ANCA), including proteinase 3 (PR3) positivity, may further complicate the clinical picture by mimicking ANCA-associated vasculitis (AAV), posing a diagnostic challenge. We present a 21-year-old male patient with a history of UC who developed rapidly progressive bilateral digital ischemia and gangrene following a recent disease flare. Laboratory evaluation revealed markedly elevated inflammatory markers and positive c-ANCA with PR3 antibodies, raising concern for AAV. Imaging demonstrated patent large vessels. Skin and renal biopsies showed no evidence of vasculitis. Despite treatment with anticoagulation, antiplatelet therapy, vasodilators, and supportive care, ischemia progressed, ultimately requiring digital and partial foot amputations. A multidisciplinary assessment supported a diagnosis of UC-associated vasculopathy after extensive evaluation excluded other causes of thrombosis. This case highlights the importance of distinguishing UC-associated vasculopathy from AAV, particularly in the setting of ANCA positivity, which can represent a diagnostic pitfall. Early tissue biopsy is essential for accurate diagnosis and appropriate management, with a multidisciplinary approach playing a critical role in guiding care.