SIBO

Definition: Small intestinal bacterial overgrowth (SIBO) is when the small intestines are colonized by excessive aerobic and anaerobic microbes that are normally found in the colon

Background:

Several disorders predispose to SIBO through alteration of the gut mucosal defenses (see below)

Intestinal motility disorders and chronic pancreatitis account for 90% of cases

• Motility Disorders - Interruption of the migrating motor complex (MMC) which clears debris from the small bowel assoc w/ IBS, Narcotic use, intestinal pseudo-obstruction, DM may predispose to SIBO
• Anatomic Disorders- Adhesions, strictures, small intestinal diverticulosis, blind loops, and reversed segment can presdispose to SIBO because of intestinal stasis
• Immune Disorders
• Gastric Hypochlorhydria - Long term PPI use or autoimmune disease
• Metabolic or systemic disorders - pancreatic insufficiency, cirrhosis, Diabetic diarrhea, Diabetic autonomic neuropathy, Celiac, Crohns

Clinical Manifestations:

• Bloating
• Flatulence
• Abd discomfort
• Chronic watery Diarrhea
• If altered anatomy, may see steatorrhea with greasy or bulky stools
• Failure to gain weight or weight loss
• Vitmain deficiency (symptoms specific to each vitamin: B12, Vit D)
• Rare cases may have altered mental status assoc w/ D-Lactic Acidosis
• Abd distension (distended fluid filled loops)
• Peripheral edema (hypoalbuminemia) *Rare*
  

Endoscopy/ Histology:

• Most patients have normal small intestine and colon
• Colitis and Ileitis in severe cases may include: mucosal edema, loss of normal vascular patterns, patchy erythema, firability, ulceration
• May also see (nonspecific): eosinophilia, villous blunting, intraepithelial lymphocytosis, cryptitis
  

Diagnosis:

• Gold Standard: Jejunal aspirate culture >10^3 colony forming units/mL (CFU/mL)
• Carbohydrate breath test using Lactulose or Glucose (Lactose and fructose can be used to test for lactose or fructose malabsorption) Sample H2, CH4, and CO2 at baseline and then every 15min after administration of either 75g glucose or 10g lactulose, the test continues for 2-4hrs
• Protocol:
• Avoid Abx for 4wks prior to test
• Prokinetic drugs and laxatives should be held for 1 wk prior to testing (to avoid false positive)
• Complex carbs and dairy should be avoided for 12hrs prior to test
• Strenuous exercise and smoking should be avoided on the day of the test
• Fast for 8-12hrs prior to test
  

Results:

• Increase in hydrogen by >20ppm above baseline within 90min is diagnostic of SIBO
• Methane level >10ppm at any point during testing is diagnostic of intestinal methanogen overgrowth (IMO) - Methanobrevibacter smithii is likely the key methanogen producer

 
If baseline hydrogen is >20ppm, may suggest poor adherence to pre-testing protocols

Constipation may increase levels of breath methane

False positive results: Rapid delivery of the test substrate to the colon (eg, in patients with short bowel syndrome)

False-negative results: occur in 30 to 40 percent of patients due to low anaerobic organism counts

Studies suggest, the glucose breath test sensitivity is 20 to 93 percent and specificity is 45 to 86 percent. The lactulose breath test had a sensitivity of 17 to 68 percent and specificity of 44 to 86 percent. Studies had several limitations. Some studies have suggested that the lactulose breath test has a slightly higher sensitivity for diagnosing SIBO as compared with the glucose breath test, others have failed to demonstrate significant differences in test performance

Treatment: (treat underlying etiology, if identified)

Initial treatment: (multiple alternatives available)

SIBO = Rifaxamin 550mg q8hrs (3x daily) for 14 days

SIBO + IMO = Neomycin 500mg BID and Rifaxamin 550mg q8hrs (3x daily) for 14 days

Correct vitamin deficiency if present

40% will have recurrence or persistence of symptoms

• Early recurrence = symptoms return <3mo after initial abx therapy - empiric treatment with second course of abx (avoid same abx used initally)
• Recurrence = symptoms >3mo after inital abx therapy - repeat breath test to confirm
• If recurrence following second course of Abx, evaluate for alternative etiology

If patient cannot tolerate abx or there is a failure to respond to abx, consider elemental diet

Additional studies looking at role of probiotics, statins, and Low FODMAP diet