Irritable Bowel Syndrome

Irritable bowel syndrome Symptoms Diagnosis Medical conditions that accompany IBS Etiology Treatment

Etiology

Initially, IBS was considered a psychosomatic illness and the involvement of biological and pathogenic factors was not verified until the 1990s, a process common in the history of emerging infectious diseases. The risk of developing IBS increases six-fold after acute gastrointestinal infection. Post-infection, further risk factors are young age, prolonged fever, anxiety and depression.

Psychosomatic illness

One of the first references to the concept of an "irritable bowel" appeared in the Rocky Mountain Medical Journal in 1950. The term was used to categorize patients who developed symptoms of diarrhea, abdominal pain, constipation, but where no well-recognized infective cause could be found. Early theories suggested that the Irritable Bowel was caused by a psychosomatic, or mental disorder. One paper from the 1980s investigated "learned illness behavior" in patients with IBS and peptic ulcers. Another study suggested that both IBS and stomach ulcer patients would benefit from 15 months of psychotherapy.Later, it would be found that most stomach ulcers were caused by a bacterial infection with Helicobacter pylori.

Additional publications suggesting the role of brain-gut "axis" appeared in the 1990s, such as a study entitled Brain-gut response to stress and cholinergic stimulation in IBS published in the Journal of Clinical Gastroenterology in 1993. A 1997 study published in Gut magazine suggested that IBS was associated with a "derailing of the brain-gut axis."

Immune reaction

From the late 1990s, research publications began identifying specific biochemical changes present in tissue biopsies and serum samples from IBS patients that suggested symptoms had an organic rather than psychosomatic cause. These studies identified cytokines and secretory products in tissues taken from IBS patients. The cytokines identified in IBS patients produce inflammation and are associated with the body's immune response.

* A study showed that intestinal biopsies from patients with constipation predominant IBS secreted higher levels of serotonin in-vitro. Serotonin plays a role in regulating gastrointestinal motility and water content, and can be altered by some diseases and infections.

* A study of rectal biopsy tissue from IBS patients showed increased levels of cellular structures involved in the production of the cytokine Interleukin 1 Beta.

* A study of blood samples from IBS patients identified elevated levels of cytokines Tumor necrosis factor-alpha, Interleukin 1, and Interleukin 6 in patients with IBS.

* A study of intestinal biopsies from IBS patients showed increased levels of protease enzymes used by the body to digest proteins, and by infectious agents to combat the host's immune system.

* A study of blood samples from IBS patients found elevated levels of antibodies to the protozoan Blastocystis.

Specific forms of immune response that have been implicated in IBS symptoms include Coeliac disease and other Food allergy conditions. Coeliac disease (also spelled "celiac") is an immunoglobulin type A-(IgA) mediated allergic response to the Gliadin protein in gluten grains, which exhibits wide variety of symptoms and can present as IBS. "Some patients with diarrhea-predominant irritable bowel syndrome (IBS-D) may have undiagnosed celiac sprue (CS). Because the symptoms of CS respond to a gluten-free diet, testing for CS in IBS may prevent years of morbidity and attendant expense.""Coeliac disease is a common finding among patients labelled as irritable bowel syndrome. In this sub-group, a gluten free diet may lead to a significant improvement in symptoms. Routine testing for coeliac disease may be indicated in all patients being evaluated for irritable bowel syndrome." Food allergies, particularly those mediated by IgE and IgG-type antibodies have been implicated in IBS.

Active infections

There is research to support IBS being caused by an as-yet undiscovered active infection. Most recently, a study has found that the antibiotic Rifaximin provides sustained relief for IBS patients. While some researchers see this as evidence that IBS is related to an undiscovered agent, others believe IBS patients suffer from overgrowth of intestinal flora and the antibiotics are effective in reducing the overgrowth (known as small intestinal bacterial overgrowth). Other researchers have focused on an unrecognized protozoal infection as a cause of IBS as certain protozoal infections occur more frequently in IBS patients. Two of the protozoa investigated have a high prevalence in industrialized countries and infect the bowel, but little is known about them as they are recently emerged pathogens.

Blastocystis is a single-celled organism which has been reported to produce symptoms of abdominal pain, constipation and diarrhea in patients, along with headaches and depression, though these reports are contested by some physicians. Studies from research hospitals in various countries have identified high Blastocystis infection rates in IBS patients, with 38% being reported from London School of Hygiene & Tropical Medicine, 47% reported from the Department of Gastroenterology at Aga Khan University in Pakistan and 18.1% reported from the Institute of Diseases and Public Health at University of Ancona in Italy. Reports from all three groups indicate a Blastocystis prevalence of approximately 7% in non-IBS patients. Researchers have noted that clinical diagnostics fail to identify infection, and Blastocystis may not respond to treatment with common antiprotozoals.