1551 The Vasculitic Mimic: Polyarteritis Nodosa Initially Presenting With Colonic Involvement

Abstract

INTRODUCTION: Polyarteritis nodosa (PAN) is a necrotizing vasculitis of the medium and small vessels which presents with gastrointestinal symptoms in up to 24.1% of patients, most commonly in the small bowel. Here we present a case of isolated colonic involvement in a patient without prior systemic immune illness or HBV. CASE DESCRIPTION/METHODS: A 62 year old man with no significant past medical history was admitted with 10 days of worsening abdominal pain and constipation. At the time of admit, labs were notable for CRP 178, leukocytosis, and creatinine 1.13. He began to pass multiple bloody, mucoid bowel movements and hemoglobin fell to as low as 6.9 g/dL, requiring transfusion. CT noted segmental colitis in the distal and sigmoid colon with proctitis. Stool pathogen panel was negative and ensuing colonoscopy showed circumferential edematous, erythematous, slightly granular mucosa from splenic flexure to rectum with areas of friability. Rectosigmoid biopsy demonstrated focal architectural distortion with a mild increase in lymphoplasmocytic inflammation and basal plasmocytosis. The patient was administered IV methylprednisolone with a prednisone taper for the presumed diagnosis of indeterminate inflammatory bowel disease (IBD). He returned 3 days later with increasing pain, tenesmus, and new findings of fever and multiple mucoid, bloody bowel movements per day. Increased stool burden proximal to the same area of colitis was seen on MRE, and colorectal surgery was consulted. Full thickness rectal biopsy revealed mucosal erosion to the muscularis layer and reactive changes thought to be due to rectal prolapse. Despite conservative therapy, he presented again 2 weeks later endorsing continued periumbilical abdominal pain, now with hgb 8.2 and WBC 18. Repeat CT showed evidence of acute appendicitis and persistent colitis, prompting emergent appendectomy with descending colostomy. Surgical pathology revealed diffuse ischemic colitis due to polyarteritis nodosa with areas of ischemic necrosis and focal bowel wall rupture in the sigmoid colon. Acute periappendicitis was also found in the appendiceal tissue, but PAN was notably absent. DISCUSSION: Delayed diagnosis of vasculitic colitis can lead to life-threatening complications. Here we present a case showing how PAN can mimic both IBD and ischemic colitis. Response to high dose steroids, the common initial treatment for both IBD flares and PAN, further confounded the diagnosis. This case highlights the need for consideration of PAN in unclear cases of colitis.