IBS

Causes

• Unsure aetiology

• Involves hypersensitive nerves of the bowel which easily upset

• Women in young 20s

• Sx come and go

Triggers

• Infection, stress, meds (abs), food FODMAPs (lactose, fructose)

• Post-infectious IBS more likely after severe gastroenteritis or foodborne illnesses

History

• Bloating / abdo pain

• Chronic diarrhoea / constipation or alternating

• Rectal urgency

• Mucous in stools

• Excess flatus

• Nausea

Examination

• Usually normal but can have mild abdo pain on palp

• May detect tenderness in the sigmoid region; exclude masses or other pathology

Alarm Features (usually req endo/colonoscopy)

• Nocturnal diarrhoea

• Weight loss

• Progressive abdo pain

• Iron def

• Rectal bleeding

• Onset over 50 yrs

• Family history IBD, colon ca

Diagnosis

• Abdo pain 1d/week for 3 months: 

  • Related to defaecation (relieved by passing wind/faeces) o Assoc with change in stool freq/form

  • Consider ROME IV criteria for functional GI disorders

Investigations

• FBC, CRP, coeliac serology, faecal calprotectin (if diarrhoea)

• Consider faeces cultures / FOBT if relevant

• Exclude IBD, coeliac, colorectal cancer in older pop, gastro esp parasites

• Thyroid function tests (exclude hyperthyroidism or hypothyroidism contributing to GI sx)

Management

Non-Pharm

• Food diary for identification of common food triggers (dietary therapy)

• Refer to dietitian for trial of a low FODMAP diet (usually post diary)

• Increase dietary fibre intake from vegetables (esp constipation)

• Adequate fluid intake of at least 2L/day

• Refer to psychologist for CBT

Pharm

• Loperamide

• Movicol

Symptom-Specific Management

Constipation

• Avoid fermentable fibres (e.g., wheat bran)

• Osmotic laxatives (e.g., lactulose) may cause bloating and pain

• Stimulant laxatives may cause cramping

Diarrhoea

• Loperamide for intermittent or pre-emptive use (e.g., at night if morning diarrhoea or before meals out)

• Non-fermentable insoluble fibre (e.g., sterculia) may be used as bulking agent

• Consider rifaximin for general sx improvement

• Specialist consideration: 5-HT3 antagonists (e.g., ondansetron)

Abdominal Pain

• Antispasmodics: 

  • Peppermint oil 0.2mL/capsule, 1-2 capsules TDS before meals o

  • Hyoscine butylbromide 20mg up to QID

  • Mebeverine 135mg TDS

• Refractory pain: Consider low-dose TCAs/SSRIs to address visceral hypersensitivity

Bloating

• Managed as for functional bloating

Psychological Therapy

• IBS often associated with anxiety or depression – treating these may improve GI sx

• Cognitive Behavioural Therapy (CBT): 

  • Useful for sx exacerbations in predictable situations (e.g., exams, public transport) 

  • Modified CBT for IBS provided by counsellors familiar with the condition

• Gut-directed hypnotherapy:

  •  Effective in refractory cases, with benefits sustained over time

Neuromodulation Using Antidepressants

• TCAs, SSRIs can be used for brain-gut neuromodulation in IBS: 

  • Effective for reducing visceral hypersensitivity, esp abdominal pain and global sx relief

• 1st Line: Low-dose TCAs (e.g., amitriptyline or nortriptyline): 

  • Start 5-10mg nocte and increase weekly as tolerated to a max of 50 mg nocte 

• Trial should continue for at least 4 weeks with full benefit taking up to 3 months

  • If sx persists despite optimal dose → stop TCA

• 2nd Line: SSRIs at standard doses if TCAs are contraindicated or ineffective, particularly for concurrent anxiety or depression

• If sx still persists → refer to gastroenterologist

Additional Notes:

• Long-term management often requires a multi-disciplinary approach, including dietitians and gastroenterologists.

• Consider probiotics in those with recurrent GI infections or those trialling FODMAP diets as adjunctive therapy.