Inflammatory cap polyps (ICP) are an extremely rare finding during digestive endoscopy, typically presenting as multiple polyps in the form of cap polyposis. Among the few reported cases of ICP, some have been associated with multiple polyposis forms, showing a clinical presentation similar to inflammatory bowel disease (IBD), which was subsequently ruled out following further diagnostic evaluation. In this report, we present an exceptionally rare case of two isolated ICPs (not in the form of cap polyposis) in a patient with a long-standing, well-established histological diagnosis of IBD located in atypical sites (specifically, the descending and transverse colon), with a characteristic endoscopic appearance. ICP can, therefore, manifest in patients with IBD and not merely be responsible for clinical presentations that require differential diagnosis from it.

Cap polyposis syndrome is a rare subtype of mucosal prolapse disease characterized by erythematous, inflammatory colonic polyps covered by a cap of fibrinopurulent mucous. Although a benign condition, patients may present with significant symptoms that can be suggestive of inflammatory bowel disease or colorectal cancer. We describe the case of a 34-year-old male who presented with a 5-month history of diarrhea and 40-lb weight loss following hospitalization for enterotoxigenic Escherichia coli colitis. The patient had a past medical history significant for prior colonoscopy revealing hundreds of polyps and a father who died of colorectal cancer at age 45. Multiple repeat infectious stool workups were negative, and antibiotics failed to resolve the patient's symptoms. The patient underwent endoscopy which revealed numerous polyps from the rectum to the terminal ileum that appeared similarly to pseudopolyps giving concern for inflammatory bowel disease. Subsequent histology demonstrated surface erosion and inflammation without dysplasia. Review of endoscopy showed inflammatory polyps with a cap of fibrinopurulent mucous. In the absence of chronic inflammation (C-reactive protein was within normal limits following hospitalization), endoscopic and histologic findings were suggestive of cap polyposis syndrome. Cap polyposis is diagnosed endoscopically and histologically. While most cases of cap polyposis are confined to the distal colon and rectum, we believe that this is the first case of cap polyposis syndrome extending to the terminal ileum. Treatment of cap polyposis syndrome is dependent on the severity of symptoms.

Cap polyposis (CP) is a rare, non-neoplastic colorectal disorder characterized by inflammatory polyps with distinctive endoscopic and histopathological features. Although increasingly reported, particularly in East Asian populations, its etiology remains unclear, and diagnostic and treatment strategies are not well standardized. Previous studies have been limited by small sample sizes and regional focus. This review aims to systematically analyze the clinical characteristics, management, and outcomes of CP in Chinese patients, with comparative insights from Japanese cases, to improve understanding and guide clinical practice. A systematic literature search was conducted in PubMed, EMBASE, Cochrane Library, CNKI, and Wanfang databases for studies published before October 2023. Keywords included "cap polyposis" and "cap-shaped polyp". Articles were screened against predefined inclusion criteria: studies from Mainland China, pathologically confirmed CP cases, and availability of clinical and therapeutic data. Data extraction and quality assessment were performed independently by two reviewers using the Newcastle-Ottawa Scale. Fourteen studies involving 57 patients were included. The most common symptoms were hematochezia (59.6%) and diarrhea (28.1%). Polyps were predominantly located in the rectum (68.4%), and 66.7% of patients had three or more polyps. Helicobacter pylori testing was positive in 57.1% of tested patients (12/21). Comparative analysis with Japanese cases revealed similar rectal predominance but suggested potential variations in gender distribution and treatment preferences. Treatments included endoscopic mucosal resection, endoscopic submucosal dissection, H. pylori eradication, and surgery. During a median follow-up of 14 months, 10 patients experienced recurrence. CP is a benign but easily misdiagnosed condition with a high recurrence rate. Diagnosis relies on combined endoscopic and histopathological findings. Treatment remains empirical, with H. pylori eradication beneficial in infected patients, and endoscopic resection effective for localized disease. Further multicenter studies are needed to establish standardized management protocols.