Small intestinal bacterial overgrowth

Small intestinal bacterial overgrowth (SIBO) is an excessive bacterial growth in the small intestine which in contrast to the large intestine in healthy individuals contains relatively small populations of bacteria.

Risk factors
Risk factors include bowel resection, bariatric surgery, disordered motility, disorders of the immune system such as IgA deficiency, low stomach acid and the use of proton pump inhibitors and immunosuppressants.

Diagnosis
SIBO can be diagnosed using a hydrogen breath test, a lactulose breath test, or a methane breath test.

Pathophysiology
Bacteria commonly implicated in SIBO include Escherichia coli, Streptococcus, Lactobacillus, Bacteroides and Enterococcus. Higher levels of Enterococcus and Stretptococcus have been found in ME/CFS patients.

Health complications
It causes increased permeability of the small intestine. It can cause malabsorption of nutrients including iron and Vitamin B12, resulting in microcytic anemia or megaloblastic anemia.

SIBO can cause a wide variety of nutritional deficiencies including Vitamin B12. It can also cause excess folic acid due to synthesis by bacteria in the small bowel.

Comorbidities
Anecdotal reports suggest a high prevalence of SIBO among CFS patients. Studies have shown that up to 80% of patients with irritable bowel syndrome have SIBO and that symptoms improve after treatment. One study found that a high number of fibromyalgia patients tested positive to a lactulose breath test, indicating SIBO, and that the degree of abnormality on the breath test correlated with the amount of pain reported.

Treatment
Standard treatment is a course of antibiotics. The best evidence for patients without constipation is for the use of rifaximin, an antibiotic that is stays in the intestine and is not absorbed in the body. Some SIBO researchers recommend adding Neomycin to rifaxamin for patients with constipation, as neomycin appears to help kill methane-producing bacteria. Some experts also recommend the use of prokinetic drugs or herbs. Some herbal treatments that have been as effective as antibiotics for eradicating SIBO.

Probiotics may also be helpful. Lactobacillus casei has been found to improve breath hydrogen scores after six weeks of treatment. There is also evidence for VSL in the treatment of SIBO. However, some probiotics may exacerbate SIBO, in particular those containing D-Lactate producing strains.