S4620 The Hidden Culprit: A Case of Appendicitis Camouflaged as Inflammatory Bowel Disease

Introduction: Appendicitis and inflammatory bowel disease (IBD) may present with overlapping clinical, radiologic, and histologic features, complicating diagnosis. Appendicitis usually causes acute right lower quadrant pain, nausea, and fever, while IBD more often presents with chronic abdominal pain, diarrhea, and weight loss. Cecal involvement may cause appendicitis to mimic IBD on imaging, with terminal ileal thickening and adjacent inflammation. Differentiating them is critical: appendicitis often needs urgent surgery, whereas IBD is treated medically. Misdiagnosis delays care and increases risk of complications. Case Description/Methods: A 24-year-old man with no significant history presented with 3 days of intermittent abdominal pain, nausea, non-bloody vomiting, fever, 2 weeks of diarrhea, poor intake, and dysuria. On admission, he was febrile and leukocytotic. Computed tomography abdomen/pelvis showed dilated bowel loops, pelvic free fluid, and terminal ileal thickening without a visible appendix—suggestive of terminal ileitis or IBD. He was given intravenous fluids, antibiotics, and empiric corticosteroids (stopped next day). Despite therapy, symptoms and inflammatory markers persisted. Repeat imaging showed a new pelvic abscess; drainage was deferred due to technical constraints. Colonoscopy to evaluate for IBD revealed erythema, edema, and bulging at the appendiceal orifice, raising concern for appendicitis. Follow-up imaging showed abscess shrinkage, and the patient improved clinically. He was discharged on oral antibiotics with elective appendectomy planned. Discussion: This case highlights challenges in distinguishing appendicitis from IBD, especially with terminal ileitis and equivocal imaging. Early steroid use, common in IBD, can worsen infections or obscure surgical pathology. Though rarely used for appendicitis, colonoscopy provided the critical clue. A multidisciplinary approach—gastroenterology, surgery, radiology—was key to diagnosis. Clinicians must consider alternatives when presentations are atypical or unresponsive. This case underscores the value of diagnostic flexibility in overlapping abdominal syndromes.