S390 Prevalence of Overlooked Gastrointestinal Disorders in Patients Diagnosed With Irritable Bowel Syndrome: A Systematic Review of Misdiagnosis and Underlying Conditions

Introduction: Patients with irritable bowel syndrome (IBS) may also carry other digestive issues that can be confused with IBS or appear along with it, causing a mistaken diagnosis. Symptoms resembling IBS can also be caused by celiac disease, bile acid malabsorption, microscopic colitis, and small intestinal bacterial overgrowth (SIBO). Figuring out these missed conditions in IBS patients matters, as they require different treatments that alleviate symptoms further than those used for general IBS. Methods: We studied articles that examined whether IBS patients had other related gastrointestinal problems. The search involved studies reported on PubMed and Embase, etc, through 2024 that look at the prevalence of celiac disease, bile acid malabsorption/diarrhea (BAD), microscopic colitis, SIBO, etc., in groups of adults with IBS. Data were collected for several patients, the tests used for diagnosis (e.g., serology/biopsy for celiac, SeHCAT for BAD, colon biopsy for microscopic colitis, breath tests for SIBO), and each diagnosis. We synthesized qualitative data to examine the evidence. Results: Multiple studies have identified specific disorders in some IBS patients. This review includes 27 studies meeting our criteria. Around 3%-4% of IBS cases may be undiagnosed celiac disease, and about 25% of IBS-D patients have unrecognized bile acid malabsorption. Microscopic colitis, especially in women and older adults, appears in over 10% of IBS-D cases. While SIBO is also common, reported rates vary widely. Though these conditions mimic IBS, each requires distinct treatment - gluten-free diets for celiac, bile acid binders for BAD, budesonide for microscopic colitis, and antibiotics for SIBO. Overlapping diagnoses are uncommon. Conclusion: A subset of IBS patients have overlooked GI conditions. In persistent IBS-D, especially in older adults, evaluation for celiac disease, bile acid diarrhea, and microscopic colitis via colon biopsy is warranted. Identifying these conditions allows for targeted treatments - such as cholestyramine or a gluten-free diet - that can significantly relieve symptoms. Given its higher prevalence in IBS, routine celiac screening is justified. Clinicians should recognize that reassessing treatment-resistant IBS can uncover treatable causes, improving care for those with functional bowel disorders.