Irritable Bowel Syndrome

IBS is one of the most frequent reasons for GI consultations in UK primary care, predominantly affecting women and those aged 20-40. It's crucial for finals to understand that IBS is a *diagnosis of exclusion*. This means serious pathologies like Inflammatory Bowel Disease (IBD), coeliac disease, and colorectal cancer *must* be ruled out before an IBS diagnosis is made. Patients typically present with chronic (often >6 months) abdominal pain related to defecation, or associated with a change in stool frequency or form. Other common symptoms include bloating (often relieved by passing flatus/stool), a feeling of incomplete evacuation, and mucus in the stool. Subtypes include IBS-C (constipation-predominant), IBS-D (diarrhoea-predominant), and IBS-M (mixed). The pathophysiology is complex, involving visceral hypersensitivity, altered gut motility, and brain-gut axis dysfunction. While not life-threatening, IBS significantly impacts a patient's quality of life. Management is holistic, progressing from lifestyle and dietary advice (e.g., reducing caffeine, alcohol, gas-producing foods) to specialist-led interventions like a low FODMAP diet. Pharmacological options target specific symptoms, with low-dose tricyclic antidepressants (TCAs) being a key second-line treatment for pain.

IBS is considered a biopsychosocial disorder. Key mechanisms include:
1. **Visceral Hypersensitivity:** Lower pain threshold to normal bowel distension, leading to exaggerated pain perception.
2. **Abnormal GI Motility:** Dysregulation of gut muscle contractions, leading to either faster (diarrhoea) or slower (constipation) transit times.
3. **Gut Microbiota Dysbiosis:** Imbalance in the gut flora, potentially contributing to inflammation and altered gut function.
4. **Brain-Gut Axis Dysfunction:** Impaired communication between the central nervous system and the enteric nervous system. Stress, anxiety, and psychological factors can significantly influence symptom perception and gut function.
5. **Post-infectious IBS:** A subset of patients develop IBS symptoms after an acute episode of gastroenteritis, suggesting a role for inflammation and altered gut permeability.

NICE criteria for IBS diagnosis (after excluding red flags and performing basic investigations): Abdominal pain for at least 6 months that is either relieved by defecation or associated with altered bowel frequency/stool form. Plus at least two of the following: altered stool passage (straining, urgency, incomplete evacuation), abdominal bloating/distension, symptoms made worse by eating, or passage of mucus.

**Crucial Red Flags (MUST rule out other pathology):**
- Age >60 with new onset bowel habit change.
- Unexplained weight loss.
- Nocturnal symptoms (waking from sleep due to symptoms).
- Rectal bleeding.
- Family history of colorectal cancer or IBD.
- Abdominal or rectal mass on examination.
- Anaemia (iron deficiency).
- Raised inflammatory markers (ESR/CRP).

Physical examination in IBS is typically normal, though mild generalised abdominal tenderness or palpable stool in the sigmoid colon may be noted. The absence of red flags and normal basic investigations are key to an IBS diagnosis.

Investigations are primarily to *exclude* other pathologies, not to diagnose IBS:
- **Bloods:**
- **Full Blood Count (FBC):** To check for anaemia (e.g., iron deficiency, a red flag for malignancy/IBD) and inflammatory markers.
- **Erythrocyte Sedimentation Rate (ESR) / C-Reactive Protein (CRP):** To rule out inflammatory conditions like IBD. A raised ESR/CRP is a red flag.
- **Coeliac Serology (Anti-TTG IgA with total IgA):** To exclude coeliac disease. A positive result requires referral for duodenal biopsy.
- **Stool Tests:**
- **Faecal Calprotectin:** A highly sensitive marker for intestinal inflammation, used to differentiate IBS from IBD (especially in younger patients). A raised calprotectin warrants further investigation (e.g., colonoscopy).
- **Stool culture/O&P:** If recent travel or infectious symptoms.
- **Further Investigations (if red flags present or initial tests abnormal):**
- **Colonoscopy:** Indicated for red flags (e.g., rectal bleeding, weight loss, family history of cancer, abnormal FBC/calprotectin) to rule out IBD or colorectal cancer.
- **CT Abdomen/Pelvis:** Rarely needed for IBS diagnosis, but may be used to investigate specific red flags or other abdominal pathology.

Management is stepwise and patient-centred:
1. **Lifestyle & Dietary Advice (First-line):**
- Regular meals, adequate fluid intake (8 cups/day).
- Limit caffeine, alcohol, fizzy drinks, and highly processed foods.
- Consider reducing gas-producing foods (e.g., beans, cabbage, onions) if bloating is prominent.
- Increase soluble fibre (e.g., oats, linseeds) for constipation, but avoid excessive insoluble fibre (e.g., bran) which can worsen bloating.
- Regular exercise.
2. **Pharmacological (Symptomatic Relief):**
- **Abdominal Pain/Spasm:** Antispasmodics (e.g., mebeverine, hyoscine butylbromide/Buscopan) taken before meals.
- **Diarrhoea:** Loperamide (taken as needed, titrate dose).
- **Constipation:** Bulk-forming laxatives (e.g., ispaghula husk). Osmotic laxatives (e.g., macrogols) can also be used. *Avoid lactulose as it often worsens bloating*.
- **Second-line for Pain:** Low-dose Tricyclic Antidepressants (TCAs) like amitriptyline (e.g., 10mg at night). These work via neuromodulation and have analgesic properties at low doses, independent of their antidepressant effect.
3. **Specialist Dietary Interventions:**
- **Low FODMAP Diet:** A restrictive diet reducing fermentable carbohydrates, supervised by a specialist dietitian. Highly effective for many, but complex to implement.
4. **Psychological Therapies:**
- Cognitive Behavioural Therapy (CBT), hypnotherapy, or psychological therapy can be very effective, especially for patients with significant psychological overlay or refractory symptoms.