Symptoms of IBS can vary widely from person to person, but most sufferers experience some degree of chronic and persistent abdominal pain, constipation, diarrhoea, or constipation alternating with diarrhoea. Other symptoms include increased amounts of mucus in the stool, gassiness, abdominal bloating (the sensation of fullness), abdominal distention (swelling), an urge to move the bowels with the inability to do so, and occasionally nausea. Symptoms commonly occur after eating a large meal or when under stress and are often temporarily relieved by having a bowel movement.
In contrast to many gastrointestinal diseases, reliable diagnostic marker or diagnostic tests are not available for IBS. Diagnosis of IBS is therefore based on the examination of symptoms and exclusion of other pathologies producing similar complaints. To facilitate this symptom-based diagnosis, an international consortium of GI specialists developed in 1988 the so called Rome criteria as a standard for the classification and diagnosis of IBS and other gastrointestinal diseases. The Rome criteria are frequently updated and adapted according to new scientific information and insights form clinical practice. The current Rome IV criteria (as of May 2016) for IBS are as follows:
“Recurrent abdominal pain on average at least 1 day a week in the last 3 months associated with two or more of the following:
- Related to defecation
- Associated with a change in a frequency of stool
- Associated with a change in form (consistency) of stool.
Symptoms must have started at least 6 months ago.”
Once diagnosed, IBS can be subdivided into one of 4 subtypes based on the usual consistency of abnormal stools associated with the symptoms above:
- IBS with constipation (IBS-C)—hard or lumpy stools ≥25% and loose (mushy) or watery stools <25% of bowel movements.
- IBS with diarrhoea (IBS-D)—loose (mushy) or watery stools ≥25% and hard or lumpy stool <25% of bowel movements.
- Mixed IBS (IBS-M)—hard or lumpy stools ≥25% and loose (mushy) or watery stools ≥25% of bowel movements.
- Unsubtyped IBS—insufficient abnormality of stool consistency to meet criteria for IBS-C, D, or M.
Thus, for example, if 25% or more of your defecations consist of hard or lumpy stool, while it is loose (mushy) less than 25% of cases, you are most likely to be assigned to the IBS-C (constipation) category. The classification of stool into hard, lumpy, watery or loose is based on the so-called Bristol stool scale (Figure 1). This scale allows for a visual assignment of stool into the following seven types:
Type Description
1 Separate hard lumps like nuts (difficult to pass)
2 Sausage shaped but lumpy
3 Like a sausage but with cracks on its surface
4 Like a sausage or snake, smooth and soft
5 Soft blobs with clear-cut edges (passed easily)
6 Fluffy pieces with ragged edges, a mushy stool
7 Watery, no solid pieces, entirely liquid
Figure 1. Bristol Stool Chart for the assessment of stool consistency. Types 1 and 2 indicate constipation, types 3-5 indicate normal stool, and types 6 and 7 indicate diarrhoea.
A particular type of IBS is the so called postinfectious IBS, which accounts for around 1 in 10 of all cases of IBS. This form of IBS is similar in symptoms but manifests following an episode of acute infectious gastroenteritis. Postinfectious IBS is also diagnosed on the basis of Rome criteria but develops following an episode of acute infectious gastroenteritis characterized by two or more of the following symptoms and findings: fever, vomiting, diarrhoea, and a positive stool culture result. Postinfectious IBS can be caused by a variety of enteric pathogens of viral, bacterial and protozoan origin, and has been documented following infection with Campylobacter species, Salmonella species, diarrhoeagenic strains of Escherichia coli, and Shigella species. Viral gastroenteritis, mostly caused by norovirus, may also cause postinfectious IBS but is less common. Although recovery may take several months and even years, patients whose IBS is post-infectious have a more favourable prognosis than those for whom the origin of the IBS is unknown. It is estimated that approximately half of all postinfectious IBS patients will return to a state of healthy digestive functioning. Recovery is less likely in patients suffering from anxiety or depression. Treatment of these emotional symptoms becomes, therefore, an important priority. Interestingly, after resolution of the initial acute infection, acute gastroenteritis may not only cause IBS but also significantly worsen intestinal symptoms in patients already suffering from IBS.
The correct subtype determination is particularly important for the targeted treatment of the main symptoms i.e. treatment of diarrhoea vs treatment of constipation. However, it should be noted that a transition between these subtypes is possible. Thus, patients suffering from constipation may experience longer periods of diarrhoea and vice versa.
Diagnosis of IBS
Diagnosis of irritable bowel syndrome usually begins with a discussion of your medical history. Here, your physician will inquire about your complaints, lifestyle (food, medication, stress, early life stress) and family history related to abdominal diseases. Any symptoms that may indicate diseases other than IBS, so called red flags, will also be discussed. These may include weight loss, rectal bleeding, fever, first-time onset of symptoms after an age of 50, nausea or recurrent vomiting, abdominal pain (especially if it’s not completely relieved by a bowel movement, or occurs at night), diarrhoea that is persistent or awakens you from sleep, anaemia due to iron deficiency. Presence of one or more of these symptoms may point to several diagnoses, such as inflammatory bowel disease, microscopic colitis, infectious colitis, small intestinal bacterial overgrowth, celiac disease, gluten sensitivity, bile acid malabsorption, and colon neoplasia, among many others. Specific tests may be then deployed to determine the precise pathology. These may include faecal tests, blood test, X-ray, gastroscopy or colonoscopy possibly with a biopsy for microscopic analysis. If, on the other hand, no red flags are detected, and other potential diseases are excluded, your physician will use the Rome criteria described above to diagnose and classify your IBS. At this stage, your physician may prescribe a treatment to alleviate the main symptoms, i.e. abdominal pain and diarrhoea or constipation. These may include dugs, diets, probiotics, food supplements such as fibres and probiotics, and several other approaches. However, IBS is a very heterogeneous disease, and responses to treatments may vary considerably between each person. Accordingly, finding what works best often requires a process of trial and error over a longer period of time. In some cases, a lack of response to treatment may also indicate a condition other than IBS. Your physician will then perform additional tests such as endoscopy, intestinal tissue biopsy, stool or blood tests, or other diagnostic procedures. Because IBS is diagnosed mainly by symptoms and specific tests are lacking, the diagnostic process as described above may vary depending on the physician. For example, even in absence of red flags suggesting other pathologies, your physician may preform several diagnostic examinations before considering IBS. Likewise, an exclusion diet and food allergy testing may be proposed to exclude food intolerance or an allergy before any IBS-specific treatment is considered.
In summary, diagnosis of IBS is largely symptom-based and is carried out by matching the patient’s symptoms to the so called Rome criteria and by excluding other pathological conditions. Once diagnosed, IBS can be classified into diarrhoea-predominant, constipation-predominant, mixed, and un-subtyped types according to the predominant stool consistency. This classification allows a targeted treatment of the main symptoms including abdominal pain, bloating and diarrhoea and/or constipation. However diagnosis of IBS is complicated by the absence specific biomarkers, high variability of both symptoms and responses to treatments, and other pathological conditions producing similar complaints. Exclusion of other conditions that produce IBS-like symptoms is therefore an integral part of an accurate diagnosis.
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