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Irritable Bowel Syndrome Causes, Signs, Symptoms, Diagnosis

Irritable Bowel Syndrome Causes, Signs, Symptoms, Diagnosis. IBS Causes, IBS Symptoms, IBS Diagnosis - www.DailyMedEd.com

Irritable Bowel Syndrome Causes, Signs, Symptoms, Diagnosis

Irritable bowel syndrome (IBS) is a functional disorder of the gastrointestinal tract characterized by chronic abdominal pain and altered bowel habits. However, only a small percentage of those affected seek medical attention.

Approximately 40% of individuals who meet diagnostic criteria for IBS do not have a formal diagnosis.

The prevalence of irritable bowel syndrome (IBS) in North America estimated from population-based studies [1,2,3,4,5,6,7] is approximately 10 to 15 %.

The estimated prevalence of IBS globally is approximately 11% with a higher prevalence in younger individuals as well as higher prevalence in women as compared with men. Women may be more likely to have constipation-predominant IBS as compared with men.

Most patients with IBS have chronic symptoms that vary in severity over time. Patients may also experience a change in IBS subtype over time with the most frequent change being from predominant constipation or diarrhea to mixed bowel habits.
Irritable Bowel Syndrome Causes

In this article we will discuss Irritable Bowel Syndrome Causes, Signs, Symptoms and Diagnosis. Irritable Bowel Syndrome triggers, diet and treatment is discussed separately in this article [coming soon!]

Irritable Bowel Syndrome Causes

Associated conditions

Irritable bowel syndrome is associated with other conditions and psychiatric disorders including:

IBS does NOT cause changes in bowel tissue or increase your risk of colorectal cancer.

Irritable Bowel Syndrome Causes

Irritable Bowel Syndrome Causes

The Irritable Bowel Syndrome causes (pathophysiology) remains uncertain. However, multiple factors that have been considered to play a role in the pathophysiology of IBS. These factors include:

  • Gastrointestinal motility: increased frequency and irregularity of luminal contractions, abnormal transit time of gastrointestinal tract have been detectable in some patients with IBS, however, no predominant pattern of motor activity has emerged as a marker for IBS.
  • Visceral hypersensitivity: selective hypersensitization (increased sensation in response to stimuli) of visceral afferent nerves in the gut has been observed in patients with IBS and is one explanation for IBS symptoms.
  • Intestinal inflammation: immunohistologic investigation has revealed mucosal immune system activation characterized by alterations in particular immune cells and markers such as lymphocytes, mast cells, proinflammatory cytockines and also higher number of tumor necrosis factor (TNF) than healthy control group in some patients with IBS.
  • Post-infection: the development of irritable bowel syndrome (IBS) following infectious enteritis has been suspected clinically based upon a history of an acute diarrheal illness preceding the onset of irritable bowel symptoms in some patients. Although the cause of bowel symptoms following acute infection is uncertain although several theories (malabsorption, increased enteroendocrine cells/lymphocytes, and antibiotic use) have been proposed. The increased risk of postinfectious IBS is associated with bacterial, protozoan, helminth infections, and viral infections.
  • Alteration in fecal microflora: the complex ecology of the fecal microflora has led to speculation whether changes in its composition could be associated with IBS.
  • Bacterial overgrowth: Small Intestinal Bacterial Overgrowth (SIBO) is associated with an increased number and/or type of bacteria in the upper gastrointestinal (GI) tract. However, data reporting an association between irritable bowel syndrome (IBS) and SIBO have been conflicting.
  • Food sensitivity: some patients with IBS report worsening of symptoms after eating and perceive food intolerance to certain foods, However, the role of food in the pathophysiology of IBS is not clear. Multiple factors have been considered to contribute to food sensitivity in patients with IBS. Investigations have centered on food specific antibodies, carbohydrate malabsorption (e.g. fructose intolerance), and gluten sensitivity.
  • Genetics: a genetic susceptibility to IBS is suggested by several twin studies [1,2,3,4], although familial patterns may also reflect underlying social factors. In addition, one study found that having a parent with IBS was a greater independent predictor of IBS than having an affected twin, suggesting that the familial nature of IBS could be due to social learning, as well as genetics. Associations between specific genes and IBS are under investigation.
  • Psychological dysfunction: psychosocial factors may influence the expression of irritable bowel syndrome (IBS). In a study of patients with symptoms of IBS or nonulcer dyspepsia, patients with gastrointestinal (GI) symptoms reported more lifetime and daily stressful events than control groups. Another study found that, compared with controls, patients with IBS exhibit increased anxiety, depression, phobias, and somatization. In a prospective study, psychosocial factors (anxiety, sleep problems, somatic symptoms) were shown to be independent risk factors for the development of IBS in a population not previously diagnosed with the condition.

Irritable Bowel Syndrome Causes

Clinical Manifestations

Irritable bowel syndrome (IBS) is characterized by chronic abdominal pain and altered bowel habits.

Chronic abdominal pain

  • Abdominal pain in IBS is usually described as a cramping sensation with variable intensity and periodic exacerbations. The location and character of the pain can vary widely and the severity of the pain may range from mild to severe.
    • The pain is frequently related to defecation. While in some patients abdominal pain is relieved with defecation, some patients report worsening of pain with defecation.
    • Emotional stress and meals may exacerbate the pain.
    • Patients with IBS also frequently report abdominal bloating and increased gas production in the form of flatulence or belching.

Altered bowel habits— Symptoms of IBS include diarrhea, constipation, alternating diarrhea and constipation, or normal bowel habits alternating with either diarrhea and/or constipation.

  • Diarrhea: is usually characterized as frequent loose stools of small to moderate volume. Bowel movements generally occur during waking hours, most often in the morning or after meals. Most bowel movements are preceded by lower abdominal cramping pain, urgency, and a sensation of incomplete evacuation or tenesmus. Approximately 50% of all patients with IBS complain of mucus discharge with stools.
    • Large volume diarrhea, bloody stools, nocturnal diarrhea, and greasy stools are not associated with IBS.
  • Constipation: stools are often hard and may be described as pellet-shaped.
    • Patients may also experience tenesmus (cramping rectal pain) even when the rectum is empty.

Irritable Bowel Syndrome Causes


Irritable bowel syndrome (IBS) should be suspected in patients with chronic abdominal pain and altered bowel habits (constipation and/or diarrhea).

A clinical diagnosis of IBS requires the fulfillment of symptom-based diagnostic criteria and a limited evaluation to exclude underlying organic disease.

Diagnostic criteria – In the absence of a biologic disease marker, several symptom-based criteria have been proposed to standardize the diagnosis of IBS. The most widely used among them are the Rome IV criteria.

  • Rome IV criteria for IBS – According to the Rome IV criteria, IBS is defined as recurrent abdominal pain, on average, at least one day per week in the last three months, associated with two or more of the following criteria:
    • Related to defecation
    • Associated with a change in stool frequency
    • Associated with a change in stool form (appearance)
  • IBS subtypes – Subtypes of IBS are recognized based on the patient’s reported predominant bowel habit on days with abnormal bowel movements. The Bristol stool form scale (BSFS) should be used to record stool consistency. Subtypes can only confidently be established when the patient is evaluated off medications used to treat bowel habit abnormalities.

Irritable Bowel Syndrome IBS subtyping and classification Bristol Stool Form Scale



IBS subtypes are defined for clinical practice as follows:

    • IBS with predominant constipation – Patient reports that abnormal bowel movements are usually constipation (type 1 and 2 in the BSFS)
    • IBS with predominant diarrhea – Patient reports that abnormal bowel movements are usually diarrhea (type 6 and 7 in the BSFS)
    • IBS with mixed bowel habits – Patient reports that abnormal bowel movements are usually both constipation and diarrhea (more than one-fourth of all the abnormal bowel movements were constipation and more than one-fourth were diarrhea)
    • IBS unclassified – Patients who meet diagnostic criteria for IBS but cannot be accurately categorized into one of the other three subtypes.


  • The Manning criteria: The likelihood of irritable bowel syndrome is proportional to the number of Manning criteria that are present. There have been conflicting data regarding the predictive ability of the Manning criteria. The criteria includes:
    • Relief of pain with bowel movements,
    • Looser and more frequent stools with onset of pain,
    • Passage of mucus,
    • Sense of incomplete emptying


  • The Kruis criteria are less frequently used in clinical practice. A number of studies have assessed the accuracy of the Rome and Manning criteria in a variety of practice settings.

As a result, some investigators continue to use the Manning criteria or a combination of both. No symptom-based criteria have ideal accuracy for diagnosing IBS; however, the Manning and Kruis criteria perform at least as well as the Rome I criteria.

Irritable Bowel Syndrome Causes

Initial evaluation

History and physical examination

The medical history serves to identify clinical manifestations of IBS as well as identify other possible causes of similar symptoms. The Bristol Stool Form Scale (BSFS) should be used to record stool consistency.

  • A thorough history with particular attention to the symptoms that are concerning for organic disease is very important.
  • The history should include exposure to a variety of medications that can cause either diarrhea or constipation. A subgroup of patients report an acute viral or bacterial gastroenteritis prior to the onset of IBS symptoms.
  • Family history assessment should include the presence of inflammatory bowel disease (IBD), colorectal cancer, and celiac disease.
  • The physical examination is usually normal in patients with IBS. However, patients may have mild abdominal tenderness to palpation. In patients with constipation a rectal examination may be useful in identifying dyssynergic defecation.

Irritable Bowel Syndrome Causes

Laboratory testing

There is no definitive diagnostic laboratory test for IBS. The purpose of laboratory testing is primarily to exclude an alternative diagnosis.

In patients with diarrhea:

  • Complete blood count (CBC)
  • Fecal calprotectin or fecal lactoferrin
  • Stool testing for giardia (antigen detection or nucleic acid amplification assay)
  • Serologic testing for celiac disease
  • C-reactive protein levels, only if fecal calprotectin and fecal lactoferrin cannot be performed

Other tests

  • Colorectal cancer screening in all age-appropriate patients.
  • Colonoscopy: to examine the entire length of the colon.
  • Flexible sigmoidoscopy: to examines the lower part of the colon (sigmoid) with a flexible, lighted tube (sigmoidoscope)
  • Abdominal X-ray and/or Abdominal CT scan: to assess for stool accumulation and determine the severity, in IBS patients with constipation.
  • Anorectal manometry and balloon expulsion testing could be done to rule out dyssynergic defecation in patients with severe constipation that is refractory to management with dietary changes and osmotic laxative therapy. 

Alarming features = additional testing
The extent of additional testing depends on the presence of alarm features. Although the presence of concerning features may identify patients more likely to have an organic disease, most patients will ultimately have a negative evaluation. Alarming features include:

  • Age of onset after age 50 years
  • Rectal bleeding or melena
  • Nocturnal diarrhea
  • Progressive abdominal pain
  • Unexplained weight loss
  • Laboratory abnormalities (iron deficiency anemia, elevated C-reactive protein or fecal calprotectin/lactoferrin)
  • Family history of IBD or colorectal cancer

Testing for Patients with alarming features

These additional evaluations are necessary to exclude other causes of similar symptoms. The diagnostic evaluation is based on the clinical presentation and usually includes:

  • Endoscopic evaluation in all patients.
  • Colonoscopy and biopsies in patients with diarrhea. Colonoscopy is done to evaluate for the presence of IBD and biopsies are obtained to exclude microscopic colitis.
  • Colonic imaging (e.g., abdominal computed tomography scan) if there is a clinical suspicion for a structural lesion.
  • Pelvic imaging with an ultrasound and/or abdominal CT scan if pain, bloating, early satiety and constipation are of recent onset in a postmenopausal woman.

Irritable Bowel Syndrome Causes

Irritable Bowel Syndrome triggers, diet and treatment is discussed separately in this article [coming soon!]

Irritable Bowel Syndrome Causes, Signs, Symptoms, Diagnosis

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