Diagnosis Of Small Intestinal Bacterial Overgrowth In Patients With Irritable Bowel Syndrome And Efficacy Of Rifaximin Treatment

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorders, which is characterized by recurrent abdominal pain or discomfort associated with alterations in stool frequency and/or consistency, for which there is no physical or biochemical cause that explains the symptoms. It is reported that 10%-20% of adults in western countries and 5%-10% adults in Asian were affected by IBS. The prevalence of IBS is on the rise year by year. It seriously affected the quality of people’s life and consumed vast medical resources. The pathogenesis and pathophysiology of IBS is complicated and still incompletely clear, while visceral hypersensitivity and abnormal gastrointestinal motility may be possible major pathophysiology, and other factors including brain-gut dysfunction, psychological disorder, dietary, gastrointestinal infection and genetics.In recent years, small intestinal bacterial overgrowth (SIBO) is receiving more and more attention, and many studies showed that the occurrence of SIBO in IBS patients was higher than healthy people. SIBO is a condition in which the small bowel is colonized by colonic bacteria may result in symptoms ranging from bloating and diarrhea to weight loss and nutritional deficiencies. However, the diagnostic tests for SIBO is still in dispute. Direct aspiration and culture of organisms is often considered as gold standard for SIBO diagnosis, formally defined by the presence of>105 colony forming units on jejunal aspiration; however this approach is invasive, difficult to perform, and aspirates from the proximal jejunum lack sensitivity in all but the most severe cases of enteric dysfunction. The lactulose hydrogen breath test (LHBT) is currently the most common used diagnostic method for SIBO, but its accuracy has been questioned by many scholars due to individual variations in small intestinal transit. LHBT combined with scintigraphic measurement of oro-caecal transit (SOCT) could distinguish rapid small intestinal transit or real SIBO and increase validity of LHBT. Our research team had previously demonstrated that 99mTc-DTPA showed better correlation with H2 rising and LHBT combined with 99mTc-DTPA is good candidate for SIBO diagnosis.The symptoms of SIBO is similar to IBS. Many studies reported that SIBO was associated with IBS and eradication of it could alleviate clinical symptoms. Rifaximin is the most commonly used antibiotic and is more effective than other antibiotics. Rifaximin is a rifamycin analogue and is a broad-range, gastrointestinal-specific antibiotic that demonstrates no clinically relevant bacterial resistance. Futhermore, it is absorbed poorly from the GI tract, and a high concentration of rifaximin is excreted in the feces as unchanged drug. It is used to treat various gastrointestinal diseases. The most likely mode of action of rifaximin is a reduction in overall bacterial load, especially in the large bowel. Although the available data suggest that a subgroup of IBS patients have a response to rifaximin, it is unclear whether this group can be identified by demographic characteristics, symptoms, or results of lactulose breath testing. Previous studies have demonstrated an association between old age, abdominal surgery, proton pump inhibitors use and SIBO, but clinical characteristics and riskfactors of IBS patients with SIBO need more researches. No study has looked at psychological distress as a moderating variable in SIBO patients. Experimental data suggest that inflammation, even if mild, could lead to persistent changes in GI nerve and smooth muscle function, resulting in colonic dysmotility, hypersensitivity, and dysfunction. Gut motility abnormalities can further predispose to bacterial overgrowth. So, it is necessary to examine whether mucosal inflamation is more severe in IBS patients with SIBO.In conclusion, based on IBS patients, the present study aimed to (1) to identify the optimal, most clinically relevant diagnostic criteria for SIBO based on LHBT alone and LHBT/SOCT. The optimal criteria for diagnosis of SIBO by LHBT/SOCT were identified by a systematic assessment of the diagnostic yield for six published diagnostic criteria; (2) the clinical relevance of SIBO diagnosis established by combined LHBT/SOCT was tested in IBS patients by comparing the clinical outcome of those with and without SIBO in a pilot study of a non-absorbable antibiotic (rifaximin) with efficacy in IBS proven in a recent double-blind, randomized, placebo-controlled trial; (3) to identify clinical features of IBS with SIBO and its correlation with psychological stress and to compare serum cytokines profiles in IBS patients with and without SIBO.The main body of the present study consists of three parts detailed below:Part Ⅰ. Investigation of optimal diagnostic criteria for SIBO based on LHBT alone and LHBT/SOCTAimby assessing six published diagnostic criteria, to identify optimal criteria for diagnosis of SIBO by LHBT/SOCT.MethodEnrolled IBS patients and healthy volunteers (HVs), all participants underwent combined LHBT with 99mTc scintigraphy. End-expiratory breath samples were collected concurrently with scintigraphic images after the meal and then every 15 min for up to 3 hours. The oro-cecal transit time (OCTT) was defined as the time at which at least 5% of administered dose of isotopes had accumulated in the caecal region. The diagnostic yields for six criteria were compared. Criteria 1:a H2 rise of ≥20ppm within 180 min; Criteria 2:a H2 rise of ≥20ppm within 90 min; Criteria 3:dual breath H2 peaks, a 12-ppm increase in breath H2 over baseline with a decrease of ≥5ppm before the second peak; Criteria 4:initial H2 rise, involving at least two consecutive values ≥5ppm above baseline, commenced at least 15 min before an increase of radioactivity (≥5% of administered dose) in the caecal region; Criteria 5:initial H2 rise, involving at least two consecutive values ≥10ppm above baseline, commenced at least 15 min before an increase of radioactivity (≥5% of administered dose) in the caecal region; Criteria 6: initial H2 rise, involving at least two consecutive values ≥20ppm above baseline, commenced at least 15 min before an increase of radioactivity (≥5% of administered dose) in the caecal region.Results① 89 IBS patients and 13 healthy volunteers were included. Patients and controls had similar age, sex and body mass index (BMI) (P>0.05).② The majority of IBS patients were diarrhea predominant (IBS-D; 70.8%) or mixed type (IBS-M; 23.6%); very few belonged to constipation predominant (IBS-C; 3.4%) and un-subtyped types (IBS-U; 2.2%).③ There was no difference in OCTT between IBS patients and healthy controls (73.8±29.1 min vs.67.7±19.6 min, p=0.433). Further, OCTT was similar in IBS-D patients and other IBS patient groups (71.9±30.9 min vs.75.0±21.2 min, p=0.628).④ In IBS patients and healthy volunteers, the incidence of SIBO by six published criteria was 75% vs.77%,31% vs.30%,44% vs.38%,39% vs.8%,17% vs.0%,3% vs.0%, successively. The 5ppm breath H2 cut-off during combined LHBT/SOCT (criteria 4) was more often positive in IBS patients than healthy controls (35/89 vs.1/13; p=0.026). This was not the case for other diagnostic criteria.Conclusion(1) SIBO is more frequent in patients with IBS as compared to healthy controls. (2) LHBT alone is not a valid test for SIBO due to variations in oro-caecal transit time. (3) However, combination of LHBT with SOCT provided an accurate and reproducible diagnostic test for SIBO. The presence of a 5ppm increase in breath H2 at least 15 minutes before the appearance of scintigraphic marker in the cecum identified a subgroup of IBS patients with SIBO.Part II. Assessment of rifaximin therapeutic effect on SIBOAimto assess rifaximin efficacy in treating IBS patients with and without SIBO according to diagnosis criteria established by combined LHBT/SOCT in Part I.MethodsIBS patients underwent combined LHBT with 99mTc scintigraphy and entered an open-label trial of oral rifaximin. All patients with a positive test result (criteria 4) and a part of patients with a negative test result were offered and prescribed this antibiotic treatment (rifaximin 600mg b.d.). Patients and investigators were blinded to the test results but not to the treatment. Before starting treatment, patients completed a questionnaire that addressed the following items:frequency and severity of abdominal pain, bloating, stool property and overall well-being. The Bristol Stool Scale was conducted to assess stool consistency and frequency. Two weeks after treatment, subjects returned for outcome assessment.Results① Of 89 IBS patients,35 were SIBO positive whereas the other 54 were SIBO negative based on criteria 4, the two groups had similar age, sex and BMI (P>0.05).② Considering the IBS subgroups, the prevalence of SIBO was higher in IBS-D than other subgroups (46.0%(29/63) vs.23.1%(6/26); p=0.044).③ IBS-D patients with SIBO reported more bloating (p=0.041); however the overall severity of symptoms was similar.④Of 89 patients,34/35 (97%) SIBO positive IBS patients and 16/54 (30%) randomly selected SIBO negative IBS patients received a therapeutic trial of antibiotic therapy and completed follow-up. Beneficial effects of rifaximin on IBS symptoms were observed in SIBO positive patients with a more significant improvement in overall severity (p=0.002). In particular, patients with IBS-D reported an improvement in abdominal symptoms including stool frequency and consistency.Conclusions(1) Rifaximin treatment alleviates symptoms in SIBO positive IBS patients including abdominal pain, bloating and overall well-being, especially in IBS-D patients, stool frequency and consistency are also significantly improved. (2) The clinical relevance of this finding is IBS patients with SIBO were likely to respond to antibiotic treatment.Part Ⅲ. Investigation of clinical characteristics of SIBO positive IBS patients and levels of serum cytokinesAimto evaluate clinical characteristics of SIBO positive IBS patients and its correlation with psychological stress, and to compare serum cytokines profiles in IBS patients with and without SIBO.MethodsIBS patients were enrolled. All the subjects underwent combined LHBT with 99mTc scintigraphy and completed standard questionnaires including general information, hospital anxiety and depression scale (HADS), and life stress events scale (LES). Blood samples were collected and serum cytokine levels (TNF-α, IL-6, IL-8, IL-10) were tested by enzyme-linked immunosorbent assay (ELISA).Results① Of 89 IBS patients,35 were SIBO positive and 54 were SIBO negative, the two groups had no significant differences in age, sex, marital status, education, average family income, job, cigarette smoking, alcohol drinking and abdominal surgery history (p>0.05).② The scores of anxiety, depression and life events were comparable in IBS patients with and without SIBO. There was no difference of psychological states in IBS patients between the two groups.③ Serum IL-10 in SIBO positive IBS patients was lower than SIBO negative patients (12.92(11.40-14.85) vs.14.03(12.66-16.33), p=0.026).Conclusions(1) Serum IL-10 in SIBO positive IBS patients was significantly lower than SIBO negative patients. (2) IBS patients with and without SIBO had no differences in age, sex, marital status, education, average family income, job, cigarette smoking, alcohol drinking and medical history. (3) There was no difference of psychological states in SIBO positive and negative IBS patients.