ABDOMINAL PAIN: A CASE OF NARROWLY±FOCUSED DIFFERENTIAL. A.K. Duncan 1 , W.E. Wysokinski 1 , A.K. Ghosh 1 ; 1 Mayo Clinic, Rochester, MN (Tracking ID #74267) LEARNING OBJECTIVES: 1) Recognize the need to expedite the work-up of poorly responding abdominal pain; 2) Recognize that vasculitis could present with diarrhea. CASE INFORMATION: A 72-year-old women was transferred to our hospital for management of her diarrhea and weight loss. Three months prior to admission, she had an episode of upper respiratory tract infection and was treated with a 10 days course of antibiotics. One month prior to entry, she developed profuse diarrhea and malaise. EGD reveled mild gastritis, small bowel follow through and colonoscopy was normal and she was empirically treated with metronidazole for pseudomembranous colitis. She complained of increasing abdominal pain and was found to have air on an upright abdominal film. Exploratory laparotomy revealed necrosis, inflammation and perforation in the small bowel and nodular lesions in the liver. She underwent extensive small bowel resection, cholecystectomy, and liver biopsy. Liver histology was reported to reveal stellate granulomata consistent with Yersinia. However, cultures and serology for Yersinia were negative. She was empirically treated with ciprofloxacin and transferred to our hospital. Examination revealed an elderly woman, with mild dyspnea, and atrial fibrillation with HR of 110/mt. She was mildly icteric, with skin breakdown in the sacral and inter-scapular region. Chest examination revealed bilateral basilar crackles. Abdomen was mildly tender and distended. Neurological examination revealed generalized but asymmetric neuropathy. Re-evaluation of the small bowel biopsy revealed transmural fibrinoid necrosis with granulomatous inflammation typical of polyarteritis nodosa (PAN). EMG was consistent with mononeuritis multiplex. ANCA was negative. Visceral angiogram revealed micro-aneurysms in the spleen, kidney, jejunal and ileal branches. She was initiated on prednisone and pulse cyclophosphamide therapy with rapid improvement in symptoms. On follow-up at 3 months she continues to gain weight and has no new symptoms. IMPLICATIONS/DISCUSSION: PAN affects the gastrointestinal tract in over 40% of cases. PAN cases presenting with acute abdomen has been associated with a high mortality (60%). GI bleeding, perforation, pancreatitis, renal insufficiency, proteinuria, cardiomyopathy and CNS vasculitis are poor prognostic factors. A high index of suspicion and re-examination of a broad differential diagnosis in cases of acute abdomen, could lead to earlier detection of PAN and successful therapy of this potentially fatal condition.