S3943 A Rare Case of Idiopathic Myointimal Hyperplasia of Mesenteric Veins Veiled as Inflammatory Bowel Disease

Introduction: Idiopathic myointimal hyperplasia of mesenteric veins (IMHMV), often misdiagnosed as inflammatory bowel disease (IBD), requires meticulous histopathologic analysis of the mesenteric vessel sampling, as early findings may be nonspecific. Case Description/Methods: A 68-year-old man with a remote history of Crohn’s disease presented with intractable abdominal pain and intermittent diarrhea. Initial work-up revealed a Norovirus positive stool sample, elevated C-reactive (CRP) protein of 3.4 mg/dL, low calprotectin; Computed tomography (CT) abdomen/pelvis with contrast noted descending and rectosigmoid colonic wall thickening with stranding concerning for undifferentiated colitis. These findings mirrored a similar episode 6 months prior that temporarily improved with supportive care. However, norovirus did not explain the chronicity of his symptoms. Thus, inpatient colonoscopy was pursued which noted erythematous, friable, ulcerative mucosa in the left colon suspicious for severe acute on chronic IBD. Empiric solumedrol 60 mg intravenous (IV) was initiated for suspected IBD; however, biopsies described active ischemic changes. CT Angiography abdomen/pelvis noted completely patent mesenteric vasculature. Despite 5 days of treatment, symptoms were unchanged, and CRP and calprotectin cyclically rose. Because of suspicion for ischemia, steroids were ultimately discontinued. A repeat flexible sigmoidoscopy noted interval improvement with healing distal rectal mucosa and improved edematous mucosa of the descending and sigmoid colon more consistent with resolving ischemia. Unfortunately, his pain regimen, peaking at 80 MME/day, was disproportionate to the mild physical exam findings. For completion, a third colonoscopy with deeper bite biopsies was performed on Hospital Day 29 highlighting dusky, necrotic, sloughing tissue from 18 to 55 cm with preserved right colonic mucosa. These pathology results were consistent with IMHMV based on the pattern of circumferential fibrin deposition and thrombus formation in the lamina propria vessels. Colorectal surgery ultimately performed a left hemicolectomy on Hospital Day 31 with concern for necrotic bowel. Post-operative course was uncomplicated, and the patient was discharged on Hospital Day 40. Discussion: Non-specific biopsies in suspected insidious courses of IBD with persistent painful proctosigmoiditis should raise suspicion for IMHMV. Increased awareness and early recognition may reduce hospital stays, symptom duration, and ineffective steroid use.