It is Time to Re-Think the Role of Small Intestinal Bacterial Overgrowth in IBS Patients

We read with great interest the debate on the use of breath testing to diagnose small intestinal bacterial overgrowth (SIBO) and the suggestion of treating with antibiotics this dysbiosis in IBS patients. Gupta and Chey have emphasized the relevance of an accurate diagnosis of SIBO in order to maximize the benefits of rifaximin and to minimize the dangerous overuse of antibiotics for wrong clinical indications. In fact, there are many investigations showing the better yield of glucose breath test (GBT) over lactulose breath test (LBT) in detecting SIBO, when compared with jejunal aspiration, because the latter examination leads substantially to an overdiagnosis of this condition in IBS. On the other hand, Pimentel proposes to treat empirically IBS patients with rifaximin, due to the fact that at present there is no valid gold standard to validate breath testing. However, all the above Authors continue to consider SIBO as one of the main causes of IBS, although many studies have strongly denied the very high prevalence (84%) found first by Pimentel et al in IBS and have questioned the role of SIBO in determining IBS symptoms. On the other hand, IBS is a common functional condition, which is characterized by abdominal pain and alterations in the consistency and frequency of stool movements, which are often associated with bloating. This clinical presentation is totally shared by SIBO and therefore it cannot be excluded that patients with this condition have only IBS-like symptoms, but do not pertain to the IBS realm. This difference can explain the good success of antibiotics in many clinical situations linked to SIBO, as we have shown in past studies, and their poor benefit in IBS (4), whose pathophysiological conditions are complex and not related to a unique mechanism. We suggest that GBT should be reserved to patients with bowel symptoms and predisposing conditions to the occurrence of SIBO, such as previous abdominal surgery (i.e. intestinal resections or cholecystectomy), prolonged acid suppressive therapy impairing the sterilizing power of acid, chronic use of antidepressant drugs capable to reduce intestinal motility, connective tissue disorders or the existence of functional constipation. In these cases, normalization of GBT after rifaximin therapy provided significant improvement of intestinal symptoms as shown in the above-mentioned clinical trials, but this success is probably due to the fact that treatment is addressed against an evident etiologic factor, which is unfortunately lacking in IBS.