Abstract
Integrative Physician Approach
Irritable bowel syndrome (IBS) is one of the most common conditions seen in physician offices today. It presents with nonspecific symptoms and is often presumptively diagnosed after ruling out conditions such as celiac disease and inflammatory bowel disease. Small intestinal bacterial overgrowth (SIBO) presents similarly to IBS and can occur concomitantly, resulting in its underdiagnosis. 1 Part of the challenge in diagnosing SIBO is its nebulous clinical presentation that includes abdominal bloating, pain, and flatulence, and in severe cases, chronic diarrhea, weight loss, and nutritional deficiencies such as vitamin A, B12, D, and E deficiency.
IBS and SIBO differ in that IBS is a functional disorder, whereas SIBO is a condition of dysbiosis in which aerobes and anaerobes colonize the small intestine, resulting in gas production and malabsorption of nutrients. Risk factors for SIBO include conditions that lead to dysbiosis: motility disorders such as gastroparesis and Parkinson's disease; anatomical disturbances such as adhesions or small bowel strictures; proton pump inhibitor use; and immune deficiencies such as HIV and immunoglobulin A deficiency. 2
To diagnose SIBO, a breath test is performed that measures exhaled gases produced by bacterial fermentation of various orally ingested substrates. The most widely used substrates are lactulose and glucose, with glucose arguably providing greater testing accuracy. The measured gases can include labeled carbon dioxide (CO2), hydrogen, and methane. We recommend measuring both hydrogen and methane, as it may increase the sensitivity of the test by capturing the 20–30% of the general population who produce methane as a main byproduct of carbohydrate fermentation. 3 To increase the accuracy of the test, it is important for patients to adhere to recommendations in terms of diet, medication, and supplements for two to four weeks before the breath test. 3 It is important to note that in studies validating breath testing, sensitivities and specificities are wide ranging, leading to controversy in the utility and interpretation of breath testing for SIBO diagnosis. 2 Other options that have been studied include empiric treatment with antibiotics and jejunal aspirate and culture. 2 However, breath testing is cost-effective, noninvasive, and widely available, and has been used in many studies both for SIBO diagnosis and as objective evidence of SIBO resolution by looking at normalization of the breath test as an outcome.
Treatment of SIBO focuses on (1) reduction of microbial burden in the small intestine via oral antibiotics or herbal preparations, and (2) addressing any underlying risk factors. Our initial approach, particularly for very symptomatic patients, is to treat patients with hydrogen predominance with the nonabsorbable antibiotic rifaximin 550 mg t.i.d. for 14 days, and those with methane predominance with neomycin 500 mg b.i.d. and rifaximin 550 mg t.i.d. for 14 days, as shown in one study to be beneficial. 4 For patients who prefer not to use pharmacologic antibiotics or for whom rifaximin may be cost prohibitive, we can consider other recommended antibiotic combinations, or give the option of treatment with antimicrobial herbal preparations such as berberine extracts of Oregon grape and coptis roots, thyme, and oregano oil. A combination of two herbal proprietary formulas was proven as effective as rifaximin in one study. 5
While probiotics are helpful in IBS, their benefit in SIBO has been controversial. However, a recent meta-analysis showed benefit in supplementing with probiotics for SIBO treatment but not prevention. 6 Recurrence of SIBO after treatment is common due to predisposing conditions. For patients with recurrence, we often presumptively treat without retesting. In those patients with relapsing disease, we will recommend rotating antimicrobial regimens for one to two weeks a month. Dietary approaches such as the FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet, SCD (specific carbohydrate diet), and GAPS (gut and psychology syndrome) diet have limited evidence in SIBO but may benefit some patients. In very severe cases, a two- to three-week trial of an elemental liquid diet that contains predigested carbohydrates, proteins, and fats may be considered. 7 In addition to pharmaceutical or herbal antibiotic therapies, treating underlying conditions is integral to SIBO treatment and prevention of recurrence.
Moreover, we emphasize the foundations of health with our patients and counsel on the brain–gut axis and the role of stress management. We educate patients on the enteric nervous system and the importance of mind–body therapies for regulation of neurotransmitters and stress hormones that impact gut function. Patients who see the impact of this whole-person approach to successfully treating the often disabling chronic symptoms of SIBO may be convinced that an integrative strategy is needed as an investment in their health going forward.