Pouchitis may develop in patients with ulcerative colitis after ileal pouch-anal anastomosis (IPAA), thereby affecting the patient’s surgical outcome and quality of life. Pouchitis usually develops after closure of an ileostomy, with a prevalence of up to 40% within 12 months after closure of the ileostomy. Symptoms In most cases, pouchitis is a nonspecific inflammation of the ileal storage pouch. The usual symptoms include increased stool frequency, urgency of stool, incontinence, nocturnal leakage, abdominal cramps, and pelvic discomfort. Fever, wasting and bloody stools are rarer. Etiology The etiology and pathogenesis of pouchitis are not fully understood. Studies suggest that it may be related to dysbiosis. Approximately 20-30% of patients with chronic pouchitis have a clear secondary etiology or predisposing factor, which is known as “secondary pouchitis”, which includes cytomegalovirus (CMV), Candida, Clostridium difficile infection (CDI), ischemia, concomitant autoimmune diseases, radiotherapy, storage bag mucosal collagen deposition, and use of non-steroidal anti-inflammatory drugs (NSAIDs). Secondary factors must often be considered in cases that are not sensitive to conventional antibiotic therapy. These secondary etiologies are carefully evaluated and treated appropriately. In most patients, storage bag inflammation and associated symptoms improve significantly after elimination of secondary etiologies. Diagnosis The diagnosis of reservoir bag inflammation requires a combination of symptom assessment, endoscopy, and histologic evaluation (PDAI). Storage pouch endoscopy is an important method used for the diagnosis and differential diagnosis of storage pouch inflammation. Gastroscopy is the tool of choice for examination because of its small diameter and high flexibility. Endoscopic manifestations of reservoir pouchitis include erythema, edema, increased nodular granulation, loss of vascular pattern, hemorrhage, brittle texture, ulceration, and erosion. Compared to endoscopy, histology has a limited role in the grading of inflammation and in the diagnosis and differential diagnosis of pouchitis. However, storage bag biopsy is still routinely performed during endoscopy. Histologic features of acute inflammation include ulceration, neutrophil infiltration, and crypt abscesses. Chronic pathologic changes such as blunted villi, crypt cell hyperplasia, and increased numbers of mononuclear cells in the lamina propria may be treated as “normal” adaptive changes in the mucosa of the pouch in response to fecal retention. These chronic pathological changes are not necessarily indicative of pouchitis. Clinical staging One of the most common classifications of pouchitis is based on response to antibiotics: antibiotic-sensitive, antibiotic-dependent, and antibiotic-resistant pouchitis. This classification has been widely accepted and is used in clinical practice and research. Antibiotic-sensitive pouchitis is characterized by episodic (<4 times/year) and effective with 2 weeks of treatment with a single antibiotic. Antibiotic-dependent pouchitis is relatively tricky, and patients often require long-term maintenance therapy for disease relief. Patients with frequent (≥4 episodes/year) or persistent symptoms of pouchitis require long-term, continuous antibiotic or probiotic therapy. Antibiotic-resistant chronic pouchitis is defined as a patient who has failed 4 weeks of antibiotic monotherapy (metronidazole or ciprofloxacin) and requires extended treatment to ≥4 weeks and the use of 2 or more antibiotics, as well as oral or topical 5-aminosalicylic acid, glucocorticoid therapy, or oral immunomodulator therapy. Treatment First-line therapeutic use of metronidazole and ciprofloxacin for storage pouch infection. In view of the adverse effects of metronidazole and ciprofloxacin and the possible risk of drug resistance with long-term use, oral rifaximin has become one of the treatment options for active pouchitis. The low bioavailability of rifaximin via gastrointestinal absorption makes it safer and reduces the risk of drug resistance, making it more suitable for the treatment of dysbiosis in pouchitis.