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Irritable Bowel Syndrome

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Overview

Irritable bowel syndrome (IBS) was previously described as a functional disorder but has recently been re-classified as a disorder of gut-brain interaction. Its pathophysiology is not fully understood but is thought to be due to changes in the gut microbiome, abnormal autonomic activity, altered central processing of afferent gut signals (‘gut-brain interactions’), and abnormal gastrointestinal (GI) motility.

Epidemiology

  • IBS is thought to affect up to 20% of the UK population
  • It is thought to be even higher as many people with symptoms do not seek medical advice
  • IBS is most commonly seen in people aged 20-39 years and prevalence decreases with increasing age
  • IBS is more common in women

Risk Factors

  • Diet:
    • Up to 90% of patients report that certain foods can trigger symptoms
    • Notable items are spicy foods, fatty foods, alcohol, and caffeine
  • GI tract infection:
    • Around 10% of people with IBS present following acute infection
  • Family history
  • Antibiotic use
  • GI tract inflammation
  • Psychological comorbidities including stress, anxiety, or depression:
    • These can influence gut-brain interactions 

Presentation

Overview

NICE recommends suspecting IBS in patients with a 6-month history of ABC symptoms:

  • Abdominal pain/discomfort:
    • The pain generally varies, which can help differentiate IBS from malignancy, where the site of pain is usually fixed
  • Bloating
  • Changes in bowel habit

Red flags and serious diseases

  • All people with IBS should be assessed for serious diseases that may present similarly:
  • Inflammatory bowel disease (IBD)
  • Bowel cancer
  • Ovarian cancer
  • Red-flag alarm symptoms should be ruled out and include:
  • Unexplained weight loss
  • Rectal bleeding
  • Iron-deficiency anaemia
  • Changes in bowel habits in patients >60 years
  • Persistent bloating in females, especially those aged >50 years
    • IBS is less likely to present for the first time in this age group and ovarian cancer may present this way
  • Abdominal or rectal masses
  • A positive faecal immunochemical test (FIT) – suggests blood in the stool
  • Family history of:

Extra-intestinal features

Some patients may have extra-intestinal features including:

Differential Diagnoses

Crohn’s disease

  • There may be associated fatigue, weight loss, fever, and rectal bleeding
  • Oral ulcers and perianal disease (e.g. skin tags, fistulae, abscesses etc.) may be present
  • An ileocaecal mass may be present
  • ESR/CRP may be elevated in acute inflammation
  • Faecal calprotectin may be positive

Ulcerative colitis

  • Patients generally have bloody diarrhoea or rectal bleeding
  • There may be faecal urgency and tenesmus
  • ESR/CRP may be elevated in acute inflammation
  • Faecal calprotectin may be positive

Coeliac disease

  • Weight loss is also generally present
  • Symptoms tend to occur with gluten ingestion
  • Iron-deficiency anaemia, low vitamin D, or hypocalcaemia may be seen, although many patients may have no abnormalities
  • Anti-TTG or anti-EMA antibodies may be positive

Colon cancer

  • Should be suspected in older patients, particularly if patients have changes in bowel habits>60 years, as IBS is less likely to present for the first time at this age
  • Patients classically have constipation with hard and small stools
  • Some patients may notice blood in their stool
  • Faecal immunochemical test (FIT) may be positive – suggesting blood in the stool
  • Iron-deficiency anaemia may be present

Ovarian cancer

  • Should be suspected where there is persistent bloating in females, especially those aged >50 years, as IBS is less likely to present for the first time at this age
  • Ovarian cancer tends to present vaguely. Other symptoms include pelvic pain, early satiety, and urinary urgency

Diverticular disease

  • More commonly seen in the elderly, around 80% of people are over the age of 85
  • Patients tend to have a chronic history of lower left quadrant pain, bloating, and changing bowel habits
  • If diverticulitis develops there may be:
    • Severe lower left abdominal pain
    • Fever
    • Malaise
    • Changes in bowel habit
    • Rectal bleeding

Small bowel bacterial overgrowth syndrome

  • May be difficult to distinguish clinically
  • Hydrogen breath testing gives positive results

Investigations

Initial tests

  • Full blood count:
    • Should be normal in IBS
    • The presence of anaemia and/or thrombocytosis suggests another diagnosis such as colorectal bleeding
  • Erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP):
    • To look for active inflammation or infection
    • Should be normal in IBS
  • Coeliac serology (e.g. anti-tissue transglutaminase (anti-TTG) or anti-endomysial antibodies (anti-EMA):
    • To exclude coeliac disease
  • Faecal calprotectin:
    • To exclude inflammatory bowel disease (IBD)

Diagnosis

Clinical diagnosis in primary care

IBS can be diagnosed if abdominal pain/discomfort has been ongoing for 6 months and the following apply:

  • Is relieved by defecation or is associated with changes in bowel frequency (increased/decreased) or stool form (e.g. loose, watery, hard, or lumpy)
  • At least 2 of the following are present:
    • Altered stool passage – such as straining, urgency, or feeling of incomplete stool passage
    • Abdominal bloating, distention, tenderness, or hardness
    • Symptoms are worse when eating
    • Passage of mucus
  • Alternative conditions with similar symptoms have been excluded, including red flags and serious conditions

Rome IV criteria

Patients may be sub-grouped into the following types using a Bristol stool chart to help direct treatment:

  • IBS with constipation (IBS-C)
  • IBS with diarrhoea (IBS-D)
  • IBS with mixed bowel habits (IBS-M)
  • IBS unclassified (IBS-U) – where symptoms to not fall into the above sub-types

Management

Initial management

Management depends on the predominant symptom:

  • For constipation: laxatives are first-line
    • Any option is appropriate except lactulose as it can increase gas production
    • Linaclotide can be considered if first-line options are insufficient
  • For diarrhoea: loperamide is first-line
  • For abdominal pain: antispasmodic agents are first-line
    • Options include direct-acting smooth muscle relaxants: mebeverine hydrochloride, alverine citrate, and peppermint oil
    • These are less likely to cause adverse effects compared with antimuscarinic drugs such as hyoscine butylbromide

Other options

  • Tricyclic antidepressants are considered 2nd-line
  • Cognitive behavioural therapy may be necessary

Patient Advice

General advice may include:

  • Having regular meals and taking time to eat
  • Eating regularly and avoiding long gaps between meals
  • Drink at least 8 cups of fluid per day, particularly water and other non-caffeinated drinks
  • Limit intake of alcohol, tea, coffee, and fizzy drinks intake
  • Limit intake of resistant starch, which is often found in processed and re-cooked foods
  • Limit intake of high-fibre foods (e.g. wholemeal or whole grains such as brown rice)
  • Avoid sorbitol, an artificial sweetener found in sugar-free sweets

Prognosis

  • Symptoms fluctuate over time and more than 50% of people continue to have symptoms after 7 years
  • A poorer prognosis is associated with a longer duration of symptoms, comorbid anxiety and depression, a history of surgery, and a higher symptom burden

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