Supplementary Material for: Phlegmonous colitis after cold snare polypectomy in an immunosuppressed patient: A case report

Introduction: Cold snare polypectomy (CSP) is a procedure with a low risk of complications. Here, we present our experience of a rare case of submucosal abscess following CSP in an immunosuppressed patient. Case presentation: 78-year-old man underwent CSP, developing a fever, chills, and right lower abdominal pain 8 days later. Ultrasound and computed tomography revealed wall thickening of the ascending colon, presenting as whitening and thickening of the same region, and excretion of pus was observed after biopsy. The diagnosis was made as phlegmonous colitis, for which antibiotic therapy was commenced. The patient was diagnosed with chronic myelomonocytic leukemia (CMML) during admission. We considered the following reasons as possible causes of infectious complications after CSP: 1) the patient had a highly immunosuppressed state with comorbidities such as CMML as well as diabetes mellitus, and 2) disruption of the mucosal barrier occurred during endoscopic resection. Conclusion: Although CSP is generally considered safe, our case highlights the potential for serious complications in immunosuppressed patients. Therefore, the decision to perform CSP in such patients should be made with caution to avoid unnecessary interventions. In instances where treatment is essential, thorough bowel preparation and prophylactic antibiotic use may be necessary to mitigate the risks.