Irritable bowel syndrome: clinical review

Irritable bowel syndrome (IBS) is a common functional gut condition accounting for 30% of gastroenterology clinic referrals.

Differences in gut microbial populations could be key in IBS (Photograph: Professors P Motta & F Carpino, University 'La Sapienza', Rome/SPL)
Differences in gut microbial populations could be key in IBS (Photograph: Professors P Motta & F Carpino, University 'La Sapienza', Rome/SPL)

Section 1: Epidemiology and aetiology

Reported prevalence in the UK ranges from 2.5% to 10.5%. This may not represent the true prevalence because not all patients seek medical attention and the absence of a diagnostic test may result in underor over-diagnosis.

IBS can affect any age group and a female preponderance is reported in most studies. An understanding of the pathogenesis is important.1


The cause of IBS remains obscure but several observations point towards a bacterial aetiology. Some studies report bacterial overgrowth as a cause and advocate antibiotic therapy; others suggest that antibiotic therapy predisposes to IBS.

Rather than focusing on one bacterial species, differences in the gut microbial population are likely to be the key triggers. This is supported by therapeutic and molecular studies. A therapeutic benefit with probiotics has been reported in several studies. Sophisticated molecular techniques are now unravelling differences in bacterial populations between IBS patients and healthy controls.

The mechanisms by which gut microbiota cause IBS are uncertain, particularly in post-infectious IBS, where the risk of IBS is related to the severity and duration of the acute gastroenteritis episode. The pathophysiological processes postulated to contribute to IBS symptoms are conceptualised in figure 1.


IBS can be classified according to predominant symptom type and severity, both of which guide therapy. Stool form classifies patients in subgroups: IBS with diarrhoea (IBS-D) or constipation (IBS-C), mixed IBS (IBS-M), or unsubtyped IBS (IBS-U).2

Severity is best judged on the extent to which symptoms interfere with daily life or affect quality of life. For audit and research, the IBS severity scoring system gives a measure by which to judge entry criteria and response to therapy. It measures severity of abdominal pain and assesses pain frequency, bloating, dissatisfaction with bowel habit and interference with life, on a visual analogue scale.

Section 2: Making the diagnosis

Diagnosis rests on eliciting positive features, and investigating alarm symptoms and subgroup symptoms.3

The cardinal symptom of IBS is abdominal pain or discomfort, typically relieved by defecation and precipitated by physiological events such as eating. Pain is accompanied by a change in frequency and/or consistency of stools.

Additional symptoms include bloating, feeling of incomplete evacuation, urgency or mucus. The Rome III criteria (see box) are useful.2

IBS coexists with other functional disorders, in particular gastro-oesophageal disease, non-ulcer dyspepsia, chronic fatigue and fibromyalgia, and each supports a diagnosis of IBS. IBS symptom subtypes are defined from the history.

Alarm symptoms warrant further investigation: weight loss, rectal bleeding, recent change in bowel habit, abdominal mass, iron deficiency anaemia, family history of colon cancer, age 50 years or over with no previous colon cancer screening, haem-positive stool.


A practical approach is to elicit symptoms of ABC – abdominal pain, bloating and change in bowel habit. Then, in the absence of alarm symptoms, investigations depend on symptom duration, severity and subtype, age, sex, family history and psychological comorbidity.3

The threshold for colonoscopy should be lowered for IBS-D with a family history of inflammatory bowel disease (IBD). Early ovarian cancer has similar symptoms to IBS and should be excluded in women >50 years.

For IBS-C, a transit study may reveal coexisting slow transit constipation amenable to biofeedback therapy. Defecating proctogram and balloon expulsion may reveal coexisting perineal abnormalities.

In patients with IBS-D, other causes of diarrhoea are considered (see case study, section 4).

Rome III criteria for diagnosing IBS

Recurrent abdominal pain or discomfort (an uncomfortable sensation not described as pain) at least three days a month in the past three months, associated with two or more of the following:

  • Improvement with defecation.
  • Onset associated with a change in frequency of stool.
  • Onset associated with a change in form (appearance) of stool.

Criteria should be fulfilled for the past three months with symptom onset at least six months before diagnosis.

Section 3: Managing the condition

Click the image to enlarge

An evidence-based approach to management is summarised in the algorithm. An important aspect is linking each reported symptom to IBS diagnostic criteria to educate patients on how a positive diagnosis is reached.

Studies have examined fibre, gluten and FODMAP (fermentable oligo-, di- and monosaccharides and polyols) intake. Soluble fibre resulted in significant symptom improvement. In contrast, insoluble fibre (bran) was associated with exacerbation of pain and flatulence.4

A gluten-free diet may help patients with IBS-D, particularly those who are HLA-DQ2/8-positive.5 The evidence for a FODMAP diet is not compelling.


A recent meta-analysis indicated that antispasmodics are more effective than placebo. When the analysis included only high-quality studies, benefit was lost.6 Antispasmodics are still worth considering, particularly where pain is mild and episodic, as side-effects are minimal. 

Loperamide reduces gut transit and may suffice to control diarrhoeal symptoms in IBS-D. There are no RCTs of laxatives in IBS, but they are commonly prescribed for IBS-C.

Most osmotic laxatives are well tolerated except for lactulose, which aggravates flatulence. Stimulant laxatives should be avoided due to risk of dependency.

Antidepressants relieve pain and other symptoms. One meta-analysis showed significant benefit with tricyclics and SSRIs, with NNTs of 4 and 3.5 respectively.7 These agents are reserved for patients with chronic or frequent symptoms. Improvement is expected in two to six weeks.

The diverse design and outcomes of trials of probiotics makes it difficult to translate their results into clinical practice, but probiotics have shown beneficial effects on pain, flatulence and bloating in most studies.

Linaclotide is showing robust efficacy for symptom improvement and resolution in IBS-C and is the only drug licensed for it. 

Psychological options

CBT or gut-focused hypnotherapy is reserved for patients with moderate or severe symptoms associated with psychological distress and impaired quality of life.8

Psychodynamic or interpersonal psychotherapy is an option where traumatic life events or coping difficulties prevail.

Section 4: Prognosis

The natural history of IBS is variable. A recent systematic review reported outcomes after a two-year median follow-up, where 30-50% of patients had stable symptoms, 2-18% had worsening symptoms and the rest reported either symptom improvement or resolution.9

However, a prospective study has reported improvement over a one-year follow-up in 50% of patients.10 Although there are no reliable prognostic predictors, one study observed that clinical improvement at three months was associated with a better prognosis at one-year follow-up.11

Follow-up aims to offer support, review response to therapy and investigate new symptoms. There is no recommended period for follow-up.

Section 5: Case study

A 23-year-old woman presented with abdominal pain, diarrhoea and mucus per rectum. The pain was relieved with defecation, triggered by eating and associated with bloating. The symptoms were restricting her lifestyle.

A previous colonoscopy showed non-specific patchy colonic inflammation. There was no response to mesalazine. Clinical examination was unremarkable. Her blood tests were normal, including CRP and a coeliac screen. Stool testing was negative. A repeat colonoscopy to terminal ileum was normal.

A positive diagnosis of IBS-D was made, supported by normal repeat investigations.

The patient was reluctant to use long-term drugs. Loperamide was effective for the diarrhoea, but not the pain. She was referred for gut-focused hypnotherapy. She completed 10 sessions and her symptoms completely resolved.

She presented again one year later. Her symptoms had recurred, but on this occasion there was associated rectal bleeding. Her CRP was raised (15mg/L). A repeat colonoscopy showed distal continuous proctitis.


The initial presenting symptoms of abdominal pain, bloating and diarrhoea fulfilled the criteria for a diagnosis of IBS.

Her predominant stool pattern defined her as IBS-D. An IBS-D subtype presentation has a wider spectrum and different conditions within the differential diagnosis than other subtypes.

The main conditions that merit exclusion within this age group are IBD, coeliac disease and giardiasis. These conditions were excluded and hypnotherapy was effective.

When this patient presented again with rectal bleeding (an alarm symptom), further investigation with colonoscopy was mandatory. On this occasion, there were changes consistent with IBD.

This case highlights the overlap in the clinical manifestation of IBS and IBD, making diagnosis difficult.

Even with a positive diagnosis of IBS, clinicians should always consider alternative diagnoses, particularly when symptoms change.

It is also noteworthy that some conditions can coexist; for example, up to 30% of patients who have IBD also have IBS.

Section 6: Evidence base

Key trials

Johnston JM, Kurtz CB, MacDougall JE et al. Linaclotide improves abdominal pain and bowel habits in a phase IIb study of patients with irritable bowel syndrome with constipation. Gastroenterol 2010; 139: 1877-86.

Linaclotide was associated with at least a 30% improvement in pain/discomfort in 55% of cases compared with 42% for placebo. Symptom resolution (for at least six of the 12 weeks of treatment) was 37% for linaclotide compared with 19% for placebo.

Chey WD, Lembo AJ, Lavins BJ et al. Linaclotide for irritable bowel syndrome with constipation. Am J Gastroenterol 2012; 107: 1702-12.

This study aimed to collate longer-term safety and efficacy data. After 26 weeks of treatment there was an improvement in pain (for at least 13 weeks) in 54% of patients on linaclotide compared with 36% on placebo, and symptom relief for at least 13 weeks in 37% of linaclotide patients, compared with 17% for placebo.


NICE. Irritable bowel syndrome in adults: diagnosis and management of irritable bowel syndrome in primary care. CG61. London, NICE, February 2008.

NICE, British Dietetic Association. Irritable bowel syndrome and diet. 2008.

Spiller R, Aziz Q, Creed F et al. Guidelines on the irritable bowel syndrome: mechanisms and practical management. Gut 2007; 56: 1770-98.

Key text

Travis SPL, Ahmad T, Collier J et al. Irritable bowel syndrome. In: Pocket Consultant Gastroenterology (third edition). Oxford, Blackwell Publishing, 2006.


Rome III criteria

Click here to take a test on this article and claim a certificate on MIMS Learning


These further action points may allow you to earn more credits by increasing the time spent and the impact achieved.

Hold a meeting with a local gastroenterologist to discuss the optimal diagnosis and treatment of IBS.

Perform a search of your patients with IBS who are being prescribed lactulose and determine if an alternative may be preferable.

Consider compiling a diet sheet for patients with IBS, to have readily available in your consulting rooms.

  • Contributed by Dr Naila Arebi, consultant gastroenterologist at The London Clinic and St Mark's Hospital, Harrow, London.


1. Arebi N, Gurmany S, Bullas D et al. Review article: the psychoneuroimmunology of irritable bowel syndrome – an exploration of interactions between psychological, neurological and immunological observations. Aliment Pharmacol Ther 2008; 28: 830-40.

2. Engsbro AL, Begtrup LM, Kjeldsen J et al. Patients suspected of irritable bowel syndrome – cross-sectional study exploring the sensitivity of Rome III criteria in primary care. Am J Gastroenterol 2013; doi: 10.1038/ajg.2013.15

3. Longstreth GF, Thompson WG, Chey WD et al. Functional bowel disorders. Gastroenterol 2006; 130: 1480-91.

4. Bijkerk CJ, de Wit NJ, Muris JW et al. Soluble or insoluble fibre in irritable bowel syndrome in primary care? BMJ 2009; 339: b3154.

5. Vazquez-Roque MI, Camilleri M, Smyrk T et al. A controlled trial of gluten-free diet in patients with irritable bowel syndrome-diarrhea: effects on bowel frequency and intestinal function. Gastroenterol 2013; doi: 10.1053/j.gastro.2013.01.049

6. Ford AC, Talley NJ, Spiegel BM et al. Effect of fibre, antispasmodics, and peppermint oil in the treatment of irritable bowel syndrome: systematic review and meta-analysis. BMJ 2008; 337: a2313. doi: 10.1136/bmj.a2313

7. Ford AC, Talley NJ, Schoenfeld PS et al. Efficacy of antidepressants and psychological therapies in irritable bowel syndrome: systematic review and meta-analysis. Gut 2009; 58(3): 367-78. doi: 10.1136/gut.2008.163162

8. Gonsalkorale WM, Miller V, Afzal A et al. Long term benefits of hypnotherapy for irritable bowel syndrome. Gut 2003; 52: 1623-9.

9. El-Serag HB, Pilgrim P, Schoenfeld P. Systemic review: natural history of irritable bowel syndrome. Aliment Pharmacol Ther 2004; 19(8): 861-70.

10. Mearin F, Badía X, Balboa A et al; RITMO Group. Predictive factors of irritable bowel syndrome improvement: 1-year prospective evaluation in 400 patients. Aliment Pharmacol Ther 2006; 23(6): 815-26.

11. Lembo T, Fullerton S, Diehl D et al. Symptom duration in patients with irritable bowel syndrome. Am J Gastroenterol 1996; 91(5): 898-905. Erratum: Am J Gastroenterol 1997; 92(8): 1409.

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