D104-14 ANCA-Negative Gastrointestinal Vasculitis Mimicking IBD: Diagnostic Challenges and Surgical Intervention

Abstract Introduction Gastrointestinal (GI) vasculitis is a rare, high morbidity condition that can mimic inflammatory bowel disease (IBD), particularly in patients lacking serologic markers such as ANCAs. It may present with abdominal pain, bleeding, or obstructive symptoms, often without systemic involvement, complicating early recognition. Clinical, laboratory, imaging, and endoscopic findings frequently overlap with IBD. Awareness of GI vasculitis is critical when fecal biomarkers indicate inflammation but serologies are negative. Case Presentation A 56-year-old male with poorly controlled diabetes and hypertension presented with severe abdominal pain. Initial evaluation revealed acute kidney injury and right-sided hydroureteronephrosis on imaging. He later developed bloating, ileus, hematochezia and a maculopapular rash. Subsequent imaging demonstrated jejunal wall thickening, mesenteric edema, and ascites. Fecal calprotectin was elevated (957 µg/g), but serologic workup was negative. Endoscopy was unremarkable. On hospital day 24, the patient developed hemorrhagic shock from GI bleeding. He underwent emergent exploratory laparotomy with small bowel resection and was admitted to the ICU after receiving massive transfusion. Rheumatology was consulted postoperatively and suspected ANCA-negative small/medium vessel vasculitis. Surgical pathology confirmed multifocal fibrinoid necrosis involving small and medium-sized vessels, for which he was started on prednisone. He later developed recurrent GI bleeding from the distal ileum. Due to high procedural risk, he was transferred to a tertiary care center. While there, a renal biopsy showed severe arterionephrosclerosis and interstitial fibrosis/tubular atrophy. The patient was placed on 40mg prednisone daily and was discharged with rheumatology follow-up. Discussion Localized GI vasculitis may occur without systemic manifestations, often delaying diagnosis and necessitating surgical intervention. While elevated fecal calprotectin and bowel wall thickening indicate inflammation, these findings are nonspecific and overlap with IBD. Imaging, including CT or MR enterography, may reveal bowel wall thickening, mesenteric edema, or ascites, further complicating differentiation. The patchy, transmural nature of vasculitis often leads to nondiagnostic superficial biopsies, emphasizing the importance of full-thickness surgical specimens for definitive diagnosis. Early consideration of vasculitis in unexplained GI inflammation, even with negative serologies, can guide prompt immunosuppressive therapy and reduce morbidity and emergent surgery. GI involvement may precede systemic manifestations, highlighting the need for vigilance in patients with unexplained hemorrhage or ischemia. This abstract is funded by: none