Overview

SIBO is a special case of dysbiosis that is characterized by an overgrowth of bacteria in the small intestines. Dr. Weyrich discusses SIBO separately from the more general topic of dysbiosis, due to the unique positioning in the alimentary cannal between the pyloric spinincter and the cecum.

Etiology

Various predisposing factors or causative factors can contribute to the development of SIBO. While not all factors may be found in an individual case, those that are present should all be addressed. These include:

  • Go to HypochlorhydriaHypochlorhydria: Stomach acid entering the small intestine through the pyloric sphincter protects against bacterial overgrowth in the small intestine; low acid levels lead to increased duodenal bacterial colonization. Causes of low stomach acid include:
  • PANCREATIC EXOCRINE INSUFFICIENCY
    • Lack of proteolytic enzymes to kill bacteria
    • Abnormal chyme in the SI affects gut motility
    • Chronic pancreatitis (30-40% have SIBO)
    • May be complicated by alcohol use
    • Cystic Fibrosis (50% have SIBO)
    • Advanced pancreatic cancer
    • [Stage2018],[Bures2010  🕮 ], [Kendig2015  🕮 ], [Singh2024].
    • Hepatobiliary Dysfunction:
      • Bile is antibacterial, so loss of normal bile flow predisposes the patient to SIBO [Bures2010  🕮 ].
    • ALTERED IMMUNITY [Stage2018]
      • Predisposes to infections and altered flora
      • Immunodeficiency syndromes including common variable immunodeficiency, AIDS, etc.
      • sIgA deficiency [Bures2010  🕮 ], [Singh2024],
      • Long term antibiotic treatment courses (Lyme, acne, RA)
      • Infectious gastroenteritis from Salmonella, Clostridium, Giardia, and some viruses; which causes functional and structural GI changes, lasting long after clearance of initial infection.
    • Reduced Gut Motility: The gut moves its content downward through the action of the MIGRATING MOTOR COMPLEX (MMC). Any disruption of this process results in reduced gut motility, which allows bacteria to linger in the small intestine, which predisposes the patient to SIBO [Bures2010  🕮 ].
      • Cytolethal distending toxin (Cdt) and its subunit CdtB are produced by some members of several bacterial species, including Campylobacter jejuni, Escherichia coli, Shigella, and Salmonella [Scuron2016  🕮 ]. Antibodies produced by the patient to CdtB cross-react with and decrease vinculin in the myenteric nerve plexi, which reduces gut motility [Kim2020  🕮 ], [Stage2018].
      • Opioid drugs also reduce gut motility.
      • Hypothyroidism reduces gut motility [Singh2024].
    • Ileocecal valve (ICV) dysfuncion: The ICV performs a critical role in preventing retrograde flow of the colonic bacteria that cause SIBO from the colon back into the small intestine.
    • ANATOMICAL ABNORMALITIES [Stage2018]
      • Can affect function of the ileocecal valve, nerve function/MMC, IgA production, and pancreatic enzyme production/secretion
      • SI strictures, adhesions (Crohn's, past surgeries, endometriosis, scleroderma), tumors
      • Short bowel syndrome, especially with removal of ileocecal valve
      • Duodenal, jejunal, colonic diverticula
      • [Bures2010  🕮 ], [Rodriguez1999  🕮 ].
    • Food Poisoning [Singh2024]
    • Overuse of Antibiotics [Singh2024]
    • Toxicity - glyphosphate [Singh2024]
    • Celiac [Singh2024]
    • DM [Singh2024]
    • Alcoholics [Singh2024]
    • Hypothyroidism [Singh2024]
    • Neurological injury [Singh2024]
    • Brain Injury [Singh2024]
    • Vagus Nerve Impairment (parasympathetic) [Singh2024]
    • Anatomical changes, ileitis, ileocecal valve reflux [Singh2024]

PROTECTIVE FACTORS

Diagnosis

SIBO is usually diagnosed by a combination of symptoms and by abnormal hydrogen or methane gas exhalation after consumption of a measured amount of glucose or lactulose. Direct sampling of small bowel bacteria via aspiration is sometimes considered the "gold standard," but this specialty test "is not readily available in most clinical settings and is limited by a high contamination rate" [Lim2023  🕮 ].

Glucose breath testing is more specific to upper small intestine (duodenem) bacterial overgrowth [cite needed] while lactulose testing is more sensitive to lower small intestine (illium) bacterial overgrowth [cite needed]. Dr. Weyrich hypothesizes that the glucose breath testing is more likely to identify problems with digestive fluid production, such as hypochlorhydria, exocrine pancreatic insufficiency, or hepatobilliary insufficiency, while the lactulose testing is more sensitive to illiocecal valve dysfunction.

Dr. Weyrich uses Go to Genova DiagnosticsGenova Diagnostics for glucose testing. At this time he has not identified an appropriate lab for lactulose testing.

Differential Diagnosis

  • Acute abdominal pain requires emergency evaluation to rule out appendicitis and other emergent conditions; chronic abdominal pain should include upper and/or lower GI tract endoscopy and possibly a CAT scan.

Treatment

Massage of the illeocecal valve is described in several YouTube videos:

References