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Understanding Irritable Bowel Syndrome (IBS): New Information

Christine Daecher, DO

In this blog post, I will be covering some new information about the evolving science of the pathophysiology of Irritable Bowel Syndrome (IBS). IBS is a common gastrointestinal disorder affecting millions of people worldwide. Chronic abdominal discomfort, altered bowel habits, and a significant impact on daily life characterize it.





What is IBS? What are the types of IBS?


IBS is currently classified as a functional gastrointestinal disorder, meaning that it involves a disruption in the normal function of the digestive system without visible structural abnormalities. The classification of IBS as functional may be changing as new evidence shows that autoimmunity and inflammation is present in at least 60% of IBS with diarrhea cases.


IBS forms are based on the predominant bowel habits:

  • IBS with constipation (IBS-C): Hard or infrequent stools.

  • IBS with diarrhea (IBS-D): Loose or frequent stools.

  • IBS with mixed bowel habits (IBS-M): Alternating episodes of constipation and diarrhea.




Common Symptoms of IBS


The symptoms of IBS vary widely from person to person, but the most commonly reported include:

  • Abdominal Pain or Cramping: Typically relieved after a bowel movement but may also be increased just before or during a BM.

  • Bloating and Gas: A feeling of fullness or pressure in the abdomen.

  • Changes in Stool Consistency: From hard, pellet-like stools to loose, watery stools.

  • Urgency or Straining: A sudden, intense need to use the restroom or difficulty passing stool.

  • Mucus in Stool: Stools may look lightly snotty or slimy with a whitish or slightly yellow material, but this is minimal


IBS does NOT include:

  • Blood in stools: either frank blood, blood on the toilet paper, or blood mixed with stools.

  • Increasing or constant pain: Cramping pain is typical of IBS, while persistent and increasing pain is worrisome.

  • Fever: A fever should never be present.

  • Large quantities of Mucus in Stools: Although mucus may be present, stools should not be overly snotty.

  • Unintentional Weight loss: IBS never causes weight loss.

  • Unexplained Anemia: Specifically, iron-deficiency anemia, but any anemia is not due to IBS.

  • A New or Sudden Change in Bowel Habits: any change in routine or pattern is concerning.

  • Onset after age 50 years. Unfortunately, the older you are when a bowel habit change occurs, the more likely colon cancer (or other malignancies) may be present.


Although gas and bloating are common symptoms of IBS, these symptoms are not part of the current criteria for diagnosing the condition. The current standard that a physician may use to diagnose IBS is called the Rome IV Criteria. Your physician may access a calculator tool that helps him or her give the probability of functional IBS being present.




A New Cause of IBS?


Let me start by focusing on IBS–D. The new way to look at this condition is to consider it SIBO or Small Intestinal Bacterial Overgrowth. It appears the condition is started by food poisoning. Approximately 10% of people who experience food poisoning will go on to develop IBS-D2. The risk for developing IBS-D was found to be higher in women who had a more severe episode of gastroenteritis and in anyone who used antibiotics for the condition2. When looking at people who have IBS-D, approximately 60% will have their condition triggered by food poisoning. The food-poisoning bacteria Campylobacter jejuni is most commonly linked as the primary trigger due to the production of bacterial toxin Cdt B (Cytolethal Distending Toxin B). E. coli, Salmonella, and Shigella bacteria also cause Cdt B to be produced. In animal studies, when Cdt B is introduced to the intestines with an infection, more than 80% of the animals experience abnormal bowel activities. Further biopsy shows increased lymphocytes in the rectum.


The problem with Cdt B is that it produces an immune reaction and antibody formation. These antibodies develop to attack the toxin and the vinculin fiber at the end of the wires of the nerve cells in the gut. This produces nerve damage to the migrating motor complex (MMC) of the gut. The MMC is the nervous system of the gut that controls the movement of food and waste through the intestines.


New studies show that 60% of IBS-D suffers have antibodies against either or both vinculin and Cdt B toxin. When the infecting bacteria do not produce Cdt B, IBS does not occur.




pathway to develop IBS-D in some people
Image courtesy of Gemelli Biotech and Mark Pimentel, MD, FRCP(C)1. From left to right, the pathway to develop IBS-D in some people is demonstrated.


More on SIBO and IBS-D


One study in which Cdt B was given to rats showed that stools had increased wet weight. When colon microflora was further examined, there was minimal change. When small intestine microflora was examined, two different abnormal clusters of bacterial changes were seen in the rats, who had a change in stools, compared to the controls, who were not given Cdt B. One cluster had an increase in E. coli that produced hydrogen. The other cluster had a rise in Desulfovirbio, a bacteria that produces hydrogen sulfide3.


In SIBO, further studies have found that small intestine bacterial cultures have found more than 50% of the microbiome to be made of the bacterial phylum of Proteobacteria3. Usually, Proteobacteria should make up about 10% of the bacteria in the small intestine microbiome. Bacteria in this phylum include Escherichia, Salmonella, Vibrio, Helicobacter, and others. The problem with the shift in microbiome flora is that Proteobacteria are carbon fermentors, meaning they ferment carbohydrates rapidly, producing a lot of gas in the upper gut.


One of the ways to diagnose SIBO is by way of breath testing. Three different gases may be tested. Hydrogen, hydrogen sulfide, and methane are abbreviated H2, HS, and CH4, respectively. H2 and HS are present in some people with IBS-D, while high levels of CH4 are associated with constipation and may be present in IBS-C.




How is IBS Diagnosed with this New Information?


As mentioned above, the current standard for diagnosing IBS is using the Rome IV Criteria. Physicians should also be prudent to rule out other conditions, including gastrointestinal malignancies, inflammatory bowel disease, and pelvic diseases.


As a functional medicine internist, when it comes to specialized testing that may be expensive and not covered by health insurance, I strive to be prudent with testing recommendations. Conventional laboratories do offer breath testing for H2 and CH4 but currently do not have available testing for HS gas. The new vinculin and Cdt B toxin antibody testing and HS breath testing are only available from the specialty laboratory, Gemelli Biotech.



References:


  1. https://youtu.be/lm3xBwfhjb0?si=LiIsBkpL8Zbkedd6

  2. Klem F, Wadhwa A, Prokop LJ, Sundt WJ, Farrugia G, Camilleri M, Singh S, Grover M. Prevalence, Risk Factors, and Outcomes of Irritable Bowel Syndrome After Infectious Enteritis: A Systematic Review and Meta-analysis. Gastroenterology. 2017 Apr;152(5):1042-1054.e1. doi: 10.1053/j.gastro.2016.12.039. Epub 2017 Jan 6. PMID: 28069350; PMCID: PMC5367939.

  3. Leite G, Rezaie A, Mathur R, Barlow GM, Rashid M, Hosseini A, Wang J, Parodi G, Villanueva-Millan MJ, Sanchez M, Morales W, Weitsman S, Pimentel M; REIMAGINE Study Group. Defining Small Intestinal Bacterial Overgrowth by Culture and High Throughput Sequencing. Clin Gastroenterol Hepatol. 2024 Feb;22(2):259-270. doi: 10.1016/j.cgh.2023.06.001. Epub 2023 Jun 12. PMID: 37315761.



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