Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. C URRENT O PINION Inflammatory bowel disease and irritable bowel syndrome: similarities and differences Giovanni Barbara, Cesare Cremon, and Vincenzo Stanghellini Purpose of review Inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) are classically viewed as dichotomous conditions. The former is perceived as a typical organic disease, and the latter is regarded as a disorder of gut function driven by mood. Recent research identified some shared contributing factors, which will be discussed here. Recent findings Mounting evidence shows the importance in both IBD and IBS of genetic, microbiological, epithelial, and immunological factors. In some instances, these factors overlap in the two conditions as shown by: involvement of brain–gut axis dysfunction in IBD, implication of TNFSF gene in Crohn’s disease and IBS, evidence of abnormal microbiota and its impact on host functions, identification of low-grade inflammation in subsets of IBS patients, and development of IBS symptoms in patients with IBD in remission. Summary IBD and IBS remain separate conditions although there are some overlapping mechanisms. Both research and clinical management would benefit from considering a functional approach for certain manifestations of IBD and accepting an organic view in subsets of IBS patients. Keywords epithelial barrier, genes, inflammatory bowel disease, irritable bowel syndrome, microbiota INTRODUCTION Inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) are frequent gastrointestinal conditions associated with a marked socioeconomic burden and impairment of patients’ quality of life (QoL) [1 & ,2 & ]. IBD and IBS are clear paradigms of the dichotomy between organic and nonorganic gastro- intestinal diseases. IBD is classically viewed as a peripheral condition characterized by intestinal inflammation, responding to therapies that primar- ily target the immune system. Conversely, IBS has been considered for a long time a centrally driven disorder diagnosed after exclusion of organic causes and manageable with lifestyle modifications and symptomatic treatment. However, several recent findings indicate that the boundaries between IBD and IBS are becoming blurred. There is epidemio- logic, genetic, immune, and microbiological over- lap. QoL is often similarly impaired in the two conditions, and it is not uncommon to verify that symptoms in patients with IBD surpass the severity of endoscopic lesions and objective markers of inflammation. The frequent experience of IBS-like symptoms in patients with IBD in remission further substantiates points of contact and fuels the mount- ing evidence supporting a role for immunological dysfunction in the pathophysiology of IBS. EPIDEMIOLOGICAL AND CLINICAL FEATURES IBD encompasses two main clinical entities, namely ulcerative colitis and Crohn’s disease, both present- ing commonly with abdominal pain, diarrhea, and bloody stools. IBS is characterized by abdominal pain/discomfort and disordered defecation and fur- ther subtyped according to bowel habit character- istics. The main subtypes are IBS with constipation (IBS-C), IBS with diarrhea (IBS-D), and IBS with Department of Medical and Surgical Sciences, University of Bologna, Bologna, Italy Correspondence to Giovanni Barbara, MD, Department of Medical and Surgical Sciences, Section of Internal Medicine and Gastroenterology, University of Bologna, St. Orsola–Malpighi Hospital, Building No. 5, Via Massarenti, 9, I-40138, Italy. E-mail: giovanni.barbara@unibo.it Curr Opin Gastroenterol 2014, 30:352–358 DOI:10.1097/MOG.0000000000000070 www.co-gastroenterology.com Volume 30  Number 4  July 2014 REVIEW