5. Irritable Bowel Syndrome

 

 

Overview

Pathophysiology

  • Classified as a disorder of gut-brain interaction (DGBI).
  • Key mechanisms:
    • Altered gastrointestinal motility.
    • Visceral hypersensitivity.
    • Gut microbiota dysbiosis.
    • Immune activation and low-grade inflammation.
    • Psychological comorbidities (anxiety, depression).
    • Dysregulated communication between the enteric and central nervous systems.

Diagnostic Criteria

Rome IV Criteria:

  • Recurrent abdominal pain, on average, at least 1 day/week in the last 3 months, associated with two or more of:
    1. Related to defecation.
    2. Associated with a change in stool frequency.
    3. Associated with a change in stool form (appearance).
  • Symptoms must have started at least 6 months prior to diagnosis.

NICE Diagnostic Criteria:

  1. Exclude other diagnoses with:
    • CRP, ESR, FBC, tTG.
  2. ABC for 6 months:
    • Abdominal pain relieved by defecation.
    • Bloating.
    • Change in bowel habit.
  3. At least two of the following:
    • Altered stool passage (straining, urgency, incomplete evacuation).
    • Abdominal bloating (more common in women), distension, tension, or hardness.
    • Symptoms made worse by eating.
    • Passage of mucus.

Clinical Features

  • Abdominal pain: Cramping, relieved or worsened by defecation.
  • Altered bowel habits: Diarrhea (IBS-D), constipation (IBS-C), mixed (IBS-M).
  • Bloating and distension.
  • Non-GI symptoms: Fatigue, sleep disturbances, anxiety, and depression.

Diagnostic Workup

Initial Investigations:

  • History and physical examination.
  • Exclusion of red flag symptoms:
    • Weight loss.
    • Nocturnal symptoms.
    • GI bleeding.
    • Family history of colorectal cancer or inflammatory bowel disease (IBD).
  • Basic lab tests:
    • Complete blood count (CBC).
    • C-reactive protein (CRP).
    • Fecal calprotectin to exclude IBD.
  • In IBS-D:
    • Test for celiac disease (tTG-IgA and total IgA).

Advanced Testing (if indicated):

  • Colonoscopy for patients >50 years or with alarm features.
  • Small intestinal bacterial overgrowth (SIBO) testing.
  • Psychological evaluation for significant comorbidities.

Management Strategies

General Approach:

  1. Patient education:
    • Explain the chronic nature of IBS and its triggers.
    • Emphasize the importance of a multidisciplinary approach.
  2. Lifestyle modifications:
    • Regular exercise.
    • Stress management (e.g., cognitive-behavioral therapy).

Dietary Management:

  • Make time for leisure, relaxation, and exercise.
  • Have regular meals and take time to eat; avoid missing meals.
  • Stay hydrated.
  • Restrict caffeine (up to 3 cups), alcohol, and fizzy drinks.
  • Limit high-fiber food (e.g., wholemeal flour, bran cereals, whole grains like brown rice).
  • Reduce intake of 'resistant starch' found in processed or reheated foods.
  • Limit fresh fruit to 3 portions per day (~80 g per portion).
  • Diarrhea: Avoid sorbitol.
  • Bloating and wind: Oats (e.g., oat-based cereal or porridge) and linseeds (up to 1 tbsp/day).
  • Avoid insoluble fiber (e.g., bran); use oats or ispaghula powder if fiber is needed.
  • Probiotics: Try for at least 4 weeks before changing.
  • Avoid: Aloe vera, acupuncture, reflexology.
  • Can try exclusion diets and single-food evidence (e.g., low FODMAP diet).

Pharmacological Treatment:

  • Antispasmodics:
    • Buscopan, peppermint oil, alverine, mebeverine (poor evidence for the 'verines).
  • Laxatives for IBS-C:
    • Avoid lactulose.
    • First-line: Fybogel or polyethylene glycol (PEG, e.g., Movicol).
    • Linaclotide (guanylate cyclase-C receptor agonist) if:
      • Optimal/max doses of previous laxatives from different classes have not helped.
      • Constipation persists for >12 months.
      • Follow up after 3 months.
  • Diarrhea:
    • Loperamide (patients can adjust doses).
    • 5-HT3 antagonists (e.g., ondansetron; RCT drugs not widely available in UK).
  • Second-line:
    • Low-dose tricyclic antidepressants (TCAs, e.g., amitriptyline 5–10 mg at night; increase as needed, max 30 mg).
    • Selective serotonin reuptake inhibitors (SSRIs) if TCAs ineffective.

Psychological Interventions:

  • Cognitive-behavioral therapy.
  • Gut-directed hypnotherapy.

Emerging Therapies:

  • Probiotics: Specific strains like Bifidobacterium infantis.
  • Microbiota-directed therapies: Fecal microbiota transplantation (experimental).

Visual Aids

Figure 1: Pathophysiological Model of IBS

  • Diagram illustrating the interplay between gut motility, microbiota, and brain-gut axis.

Table 1: Pharmacological Options for IBS

Symptom

First-line Therapy

Second-line Therapy

IBS-C

Psyllium, PEG

Linaclotide, Lubiprostone

IBS-D

Loperamide

Eluxadoline, Bile acid agents

Abdominal Pain

Antispasmodics

TCAs, SSRIs

References

  1. Chey WD, et al. Irritable bowel syndrome: A clinical review. JAMA. 2015;313(9):949-58. Link
  2. British Society of Gastroenterology. Guidelines on the management of IBS. Gut. 2021;70(7):1214-1240. Link
  3. NICE. Irritable bowel syndrome in adults: diagnosis and management. NICE guidelines CG61. Updated 2017. Link