Small bowel overgrowth

Results in exaggerated inflammation and gastrointestinal symptoms.

Can manifest as gas related symptoms.

Associated with the small bowel diverticula, and scrictures due to the Crohn’s disease, radiation or nonsteroidal anti-inflammatory drugs.

Other causes include malignancy, Crohn’s disease, diverticula in the small intestine, intestinal resections, motility disorders, diabetes, scleroderma, IgA deficiency. and hernias.

Associated with Roux-en-Y surgery and ileoecal valve resection.

Associated with dysmotility scleroderma, narcotics, diabetes mellitus, and amyloidosis.

Associated with achlorhydria, gastric resection, atrophic gastritis, and advancing age.

Associated with celiac disease, cirrhosis, immunodeficiency and pancreatic insufficiency.

Associated with PPI use.

There are 500-1000 bacterial species that reside in the bowel.

Small intestinal bacterial overgrowth

Refers to a disorder of excessive bacterial growth in the small intestine.

Unlike the colon, which is rich with bacteria, the small bowel usually has fewer than 10,000 organisms per millilitre.

With bacterial overgrowth typical symptoms include: nausea, bloating, vomiting, diarrhea, malnutrition, weight loss and malabsorption.

The diagnosis of bacterial overgrowth is made by aspiration from the jejunum that grows in excess of 105 bacteria per millilitre.

Risk factors for the development of bacterial overgrowth include: dysmotility; anatomical disturbances in the bowel, including fistulae, diverticula and blind loops created after surgery, and resection of the ileo-cecal valve, gastroenteritis-induced alterations to the small intestine, and the use of certain medications, including proton pump inhibitors.

It is treated with an elemental diet or antibiotics, which may be given in a cyclic fashion to prevent tolerance to the antibiotics, sometimes followed by prokinetic drugs to prevent recurrence if dysmotility is a suspected cause.

Deficiency of vitamin B12 can occur in bacterial overgrowth.

Many symptoms of small intestinal bacterial overgrowth are due to malabsorption of nutrients due to the bacteria which either metabolize nutrients or cause inflammation of the small bowel, impairing absorption.

Symptoms include: nausea, flatus, constipation, bloating, abdominal distension, abdominal pain or discomfort, diarrhea, fatigue, and weakness.

Causes an increased permeability of the small intestine, weight loss, malnutrition and children may have difficulty attaining proper growth.

Steatorrhea, may occur.

With longstanding disease one can develop complications due to malabsorption of nutrients.

Anemia may occur from a variety of mechanisms, as many of the nutrients necessary for RBC production are absorbed in the affected small bowel.

Malabsorption of iron from the more proximal parts of the small bowel, the duodenum and jejunum, can lead to the develop a microcytic anemia.

Vitamin B12 is absorbed in the ileum, and patients who malabsorb vitamin B12 can develop a megaloblastic anemia.

It is associated with a higher frequency of diarrhea, a lower body mass index, and a lower serum albumin concentration.

The ileocecal valve prevents reflux of bacteria from the colon into the small bowel, and its removal can lead to bacterial overgrowth.

Risk factors for development of bacterial overgrowth include:

Certain people are more predisposed to the development of bacterial overgrowth because of certain risk factors including motility disorders, anatomical problems or immune disorders.

Problems with motility may either be diffuse, or localized and include diseases like scleroderma and possibly celiac disease causing diffuse slowing of the bowel, leading to increased bacterial concentrations.

More commonly, the small bowel may have anatomical abnormalities, diverticula, that can cause bacteria to accumulate.

After surgery involving the stomach and duodenum, a blind loop may be formed, leading to stasis of flow of intestinal contents, causing overgrowth, the blind loop syndrome.

Other causes of bacterial overgrowth include disorders of the immune system. chronic pancreatitis, use of immunosuppressant medications, immunodeficiency conditions, such as common variable immunodeficiency, IgA deficiency, and hypogammaglobulinemia, abnormal connections between the bacteria-rich colon and the small bowel can increase the bacterial load in the small bowel,

Patients with diseases of the ileum may require surgery that removes the ileocecal valve connecting the small and large bowel and an lead to reflux of bacteria into the small bowel.

Surgical connections between the stomach and the ileum for weight loss may increase bacterial load in the small bowel.

Proton pump inhibitors used to reduce stomach acid, is associated with an increased risk of developing SIBO.

The usual methodology to study SIBO involves the use of breath testing as an indirect study.

Studies suggest up to 80% of patients with irritable bowel syndrome have SIBO, and reduction in IBS symptoms following therapy for SIBO is common.

Lactulose breath testing has shown that patients with fibromyalgia have a more pronounced degree of abnormal results compared to both IBS patients and the general population.

There is a positive correlation between the amount of pain and the degree of abnormality on the breath test.

There is an increased prevalence of intestinal hyperpermeability that occurs commonly with SIBO.

Intestinal bacteria may play an causal role in rosacea: significantly more patients are hydrogen-positive than controls indicating the presence of bacterial overgrowth (47% v. 5%).

Hydrogen-positive patients given a 10-day course of rifaximin, 96% of patients experienced a complete remission of rosacea symptoms that lasts beyond 9 months.

In some rosacea patients that tested hydrogen-negative were still positive for bacterial overgrowth when using a methane breath test instead.

These patients showed little improvement with rifaximin, but experienced clearance of rosacea and normalization of methane excretion following administration of metronidazole, which is effective at targeting methanogenic intestinal bacteria.

Symptoms may be reduced in some patients when given a reduced carbohydrate diet, as such a diet restricts available material necessary for bacterial fermentation and thereby reduce intestinal bacterial populations.

Certain species of bacteria are more commonly found in aspirates of the jejunum taken from patients with bacterial overgrowth.

These bacteria include: Escherichia coli, Streptococcus, Lactobacillus, Bacteroides, and Enterococcus species.

There are 500-1000 different species of bacteria that reside in the bowel.

If the flora of the small bowel is altered, inflammation or impaired digestion can occur.

Chronic diarrhea may be associated with bacterial overgrowth as contributor to their symptoms.

Diarrhea in bacterial overgrowth causes include: excessive bacterial concentrations causing inflammation of the small bowel, with inflammatory diarrhea, malabsorption of lipids, proteins and carbohydrates causing poorly digested products, causing osmotic diarrhea, and stimulation of secretory mechanisms of colonic cells, leading to a secretory diarrhea.

Can sometimes be initiated by an acute gastrointestinal infection.

Diagnostic aspiration from the jejunum is the best procedure for diagnosis.

A bacterial load of greater than 105 bacteria per millilitre is diagnostic for bacterial overgrowth.

Malabsorption can be detected by the D-xylose test.

Xylose is a sugar that does not require enzymes to be digested.

The D-xylose test involves drinking D-xylose, and measuring levels in the urine and blood

Absence of D-xylose in the urine and blood, suggests that the small bowel itself is not absorbing properly, as opposed to problems with enzymes required for digestion.

The normal small bowel has less than 104 bacteria per millilitre.

Some consider aspiration of more than 103 positive if the flora is predominately colonic type bacteria as these types of bacteria are considered pathological in excessive numbers in the small intestine.

Aspiration results in the diagnosis of SIBO has a reproducibility that can be as low as 38 percent.

Breath tests have a high rate of false positive.

Biopsies of the small bowel in bacterial overgrowth can mimic celiac disease, being associated with partial villous atrophy.

Breath tests for bacterial overgrowth, are based on bacterial metabolism of carbohydrates to hydrogen and/or methane, or based on the detection of by-products of digestion of carbohydrates that are not usually metabolized.

The hydrogen breath test involves having the patient fast for a minimum of 12 hours then having them drink a substrate usually glucose or lactulose, then measuring expired hydrogen and methane concentrations typically over a period of 2–3 hours.

The hydrogen breath test compares well to jejunal aspirates in making the diagnosis of bacterial overgrowth.

Tests also available based on the bacterial metabolism of D-xylose.

Increased bacterial concentrations are also involved in the deconjugation of bile acids.

The glycocholic acid breath test involves the administration of the bile acid 14C glychocholic acid, and the detection of 14CO2, is elevated in bacterial overgrowth.

Biopsies of the small bowel in bacterial overgrowth can mimic those of celiac disease, with blunting of villi, hyperplasia of crypts and an increased number of lymphocytes in the lamina propria.

Some believe physicians suggest that the best diagnostic test is a trial of treatment. If the symptoms improve, an empiric diagnosis of bacterial overgrowth can be made.

Small bowel bacterial overgrowth is usually treated with a course of antibiotics.

Some experts recommend probiotics as first line therapy with antibiotics being reserved as a second line treatment for more severe cases.

A variety of antibiotics, including tetracycline, amoxicillin-clavulanate, fluoroquinolones, metronidazole, neomycin, cephalexin have been used; however, the most efficacious is rifaximin.

One week of antibiotics is usually sufficient to treat the condition.

Antibiotics can be given in a cyclical fashion in order to prevent recurrence and tolerance.

Any predisposing conditions should also be treated.

Probiotics alter the bacterial flora in the bowel to cause a beneficial effect.

Lactobacillus casei has been found to be effective in improving breath hydrogen scores after 6 weeks of treatment presumably by suppressing levels of a small intestinal bacterial overgrowth of fermenting bacteria.

Probiotics are superior to antibiotics in the treatment of SIBO.

A combination of probiotics has been found to produce better results than therapy with the antibiotic drug metronidazole.

Probiotics have been found to be effective in treating and preventing secondary lactase deficiency and small intestinal bacteria overgrowth in individuals suffering from post-infectious irritable bowel syndrome.

Probiotics taken in uncomplicated cases of SIBO can usually result in the individual becoming symptom free.

Probiotic therapy may need to be taken continuously to prevent the return of overgrowth of gas producing bacteria.

An elemental diet taken for two weeks provides nutrition for the individual while depriving the bacteria of a food source, and can be an alternative treatment.

Additional treatments include: the use of prokinetic drugs such as 5-HT4 receptor agonists or motilin agonists to extend the SIBO free period after treatment with an elemental diet or antibiotics.

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