Objective: To investigate the prevalence and clinical features of small intestinal bacterial overgrowth (SIBO) in diarrhea-predominant irritable bowel syndrome (IBS-D) patients detected by hydrogen and methane in lactulose breath test (LBT), and to study the effects of rifaximin in IBS-D patients.
Methods: Consecutive patients with IBS-D who met Rome Ⅲ criteria, and gender- and age-matched healthy volunteers were enrolled from March 2015 to January 2016 in Peking University Third Hospital. All the ISB-D patients underwent LBT to detect the prevalence of SIBO. The clinical and LBT features of IBS with SIBO (IBS-P group) and without SIBO (IBS-N group) were analyzed. The effects of rifaximin therapy (0.4 g, twice per day for 4 weeks) in IBS-D patients were evaluated by comparing changes in clinical features and LBT results after treatment.
Results: (1) Eighty-four IBS-D patients and 22 healthy controls were enrolled. The prevalence of SIBO in IBS-D patients was 41.67% (35/84), with 27 (77.14%) only hydrogen-positive, 5 (14.29%) methane-positive, and 3 (8.57%) both methane- and hydrogen-positive. (2) The body mass index (BMI) in the IBS-P group was lower than in the IBS-N group [(21.61±0.57) vs (23.44±0.54) kg/m(2,) P<0.05], the maximum stool frequency was also less than in the IBS-N group [(3.85±0.23) vs (4.88±0.35) times/day, P<0.05]. (3) No significant difference was found in oro-cecal transit time (OCTT) among IBS-P, IBS-N and healthy controls. The hydrogen concentration in small intestinal and colonic sections in breath of the IBS-P group was higher than that of both healthy controls and the IBS-N group, while methane concentration in small intestinal and colonic sections (160 min) was higher than that of the IBS-N group (all P<0.05). (4) There was no linear relationship between mean hydrogen and methane concentrations in LBT among the IBS-P, the IBS-N and healthy control groups (all r<0.35, P>0.05). (5) Totally 13 IBS-P patients received rifaximin therapy, in whom the symptoms of abdomen pain, bloating, fecal consistency, stool frequency, and stool satisfactory were significantly improved after treatment (all P<0.05); 8 IBS-N patients received rifaximin therapy, in whom fecal consistency, stool frequency, and satisfactory were significantly improved (all P<0.05). (6) And 5/13 of the IBS-P patients receiving rifaximin presented negative LBT results after rifaximin therapy, with lower hydrogen concentration at all the time points, especially in colonic section (120 min) [(34.54±7.32) ×10(-6) vs (52.23±9.40) ×10(-6,) P<0.05] and lower methane concentration especially in small intestinal section (80 min) [(8.54±0.95) ×10(-6) vs (11.31±0.94) ×10(-6,) P<0.05].
Conclusions: About 41.67% of the IBS-D patients meeting Rome Ⅲ criteria have SIBO, which can be better screened by combining hydrogen and methane in LBT compared with only hydrogen in LBT. SIBO can affect nutritional status in IBS-D patients. Rifaximin can improve the systematic symptoms of IBS-D patients with SIBO, also reduce hydrogen and methane concentration in breath, while only improving diarrhea in IBS-D patients without SIBO. Some differences in gut microbiota may exist between IBS-D with and without SIBO.