Irritable Bowel Syndrome

Introduction

Irritable Bowel Syndrome (IBS) is a functional gastrointestinal disorder characterised by chronic abdominal pain or discomfort, bloating, and altered bowel habits (diarrhoea, constipation, or both), without any identifiable structural or biochemical abnormality. Symptoms are due to abnormal motility, visceral hypersensitivity, and gut–brain axis dysfunction.

Peak Incidence

• Most common between 20 and 40 years of age.
• More prevalent in women.

Symptoms

• Diarrhoea or constipation (or alternating between the two)
• Abdominal pain, often relieved by defecation
• Bloating – especially common in women
• Symptoms worsen after eating
• Symptoms improve after opening the bowels

Signs

• Altered stool passage – straining, urgency, or incomplete evacuation
• Abdominal bloating, distension, tension, or hardness
• Mucus in stool
• No alarm features or systemic signs

Diagnosis

IBS is a clinical diagnosis based on NICE guidance, typically made when symptoms have been present for at least 6 months.

Key diagnostic features (ABC):

• Abdominal pain or discomfort
• Bloating
• Change in bowel habit

A positive diagnosis can be made if:

• Abdominal pain is relieved by defecation, or
• Pain is associated with a change in bowel frequency or stool form

Investigations to Exclude Other Conditions

IBS is a diagnosis of exclusion. The following tests are recommended to rule out other causes:

• FBC, ESR, CRP – To rule out inflammatory or anaemic causes
• Coeliac screen – Tissue transglutaminase (anti-TTG) antibodies and total IgA
• CA125 – In women with symptoms suggestive of ovarian cancer
• Faecal calprotectin – To exclude inflammatory bowel disease (IBD)
• FIT (Faecal Immunochemical Test) – In adults over 60 with change in bowel habit to rule out bowel cancer

Red flag features – consider alternative diagnoses if present:

• Unintentional weight loss
• Rectal bleeding
• New onset symptoms in patients aged 60 years or older
• Family history of bowel or ovarian cancer

Complications

• Haemorrhoids – Due to chronic constipation and straining
• Anxiety and depression – Often co-exist with or exacerbated by IBS
• Impaired quality of life
• Adverse medication effects
• Social withdrawal – Due to unpredictable bowel symptoms

Management

Lifestyle and Dietary Measures

• Maintain adequate hydration
• Eat regular small meals
• Limit caffeine (≤3 cups/day) and alcohol
• Reduce processed foods and high-fat meals
• Trial of a low FODMAP diet (under dietetic supervision)

First-Line Medications

• Loperamide – For diarrhoea
• Laxatives – For constipation (avoid lactulose, which worsens bloating)
• Antispasmodics – For pain relief (e.g. hyoscine butylbromide, mebeverine)

Second-Line Treatment

• Low-dose tricyclic antidepressants (TCAs)
  • e.g. Amitriptyline 5–10 mg at night

Third-Line Treatment

• Selective serotonin reuptake inhibitors (SSRIs) – If TCAs are ineffective

• Psychological therapies

  • Cognitive behavioural therapy (CBT)
  • Hypnotherapy
  • Psychotherapy for refractory cases