Irritable bowel syndrome (IBS) is a chronic condition that is predominantly a condition that causes abdominal pain (relieved when opening bowels) and has an associated change in bowel habits. It is a functional bowel disorder meaning there is no disease (such as infection or inflammation) underlying that is causing the issue and the issue solely lies within the dysfunction of the bowel.
🏘 Epidemiology
It accounts for up to 50% of referred patients to gastroenterologists within the UK, with a total prevalence of 17%.
It is more prevalent in women (23%) than in men (11%), however, this may be a result of women outnumbering men in seeking physician help for IBS at a 2:1 ratio.
It usually presents in adolescence or early adulthood.
Pathophysiology
The pathophysiology is not completely understood at this point, however, for the most part it seems to be an issue involving the motor and sensory portions of the GI tract. The gut reacts differently in response to some stimuli. These stimuli may be luminal (foods, bacteria, toxins) or it may be environmental (stress or abuse). This can then lead to dysmotility as well as pain. However, there seems to be no change in the histology of the large and small intestines. An immune component may be involved based on some subtle findings but the verdict is still out as for the exact cause of IBS (if there even is one).
🔢 Classification
The Rome IV sub-typing of IBS is based on the predominant stool pattern seen:
- IBS with constipation (IBS-C) - hard/lumpy stools for >25% of bowel movements with loose/watery stools <25% of bowel movements.
- IBS with diarrhoea (IBS-D) - loose/watery stools for >25% of bowel movements with hard/lumpy stools <25% of bowel movements.
- MIxed IBS (IBS-M) - hard/lumpy stools <25% of bowel movements with loose/watery stools for <25% of bowel movements as well.
- Unspecified IBS - does not meet any of the criteria.
⚠️ Risk factors
- Female gender - 2:1 ratio.
- <50 years old - adolescence or early adulthood is most common.
- Previous enteric infection - 30% of patients develop IBS after acute bacterial gastroenteritis.
- Family history - 2.75x higher if a 1º relative has IBS.
- PTSD - 2.80 increased odds ratio.
- Physical and sexual abuse
😷 Presentation
We should consider IBS if a patient presents with classic ABC features for the past 6 months:
- A - Abdominal pain: normally cramping feeling in the lower/mid-abdomen.
- B - Bloating: improved with defecation or flatulence.
- C - Changes in bowel habits: diarrhoea or constipation or fluctuation between constipation and diarrhoea.
Symptoms are often worse after eating and improved with opening bowels.
🔍 Investigations
NICE guidance is in accordance with the Manning criteria (mentioned below):
A diagnosis of IBS should be considered only if the person has abdominal pain or discomfort that is either relieved by defecation OR associated with altered bowel frequency or stool form. This should be accompanied by at least 2 of the following 4 symptoms:
- Altered stool passage - straining, urgency or incomplete evacuation.
- Bloating, distension, tension, hardness
- Worsened by eating
- Passage of mucus
If diagnosis criteria are met, we need to perform the following tests:
- FBC, ESR, CRP - to exclude any inflammatory or malignant causes. If anaemia is present, or FBC count is raised then non-IBS disease should be considered.
- Faecal calprotectin - to exclude IBD (good marker of inflammation within the bowel specifically).
- Negative coeliac disease serology - anti-TTG or anti-EMA antibodies.
- Cancer is not suspected
Manning criteria
Used in primary care.
A diagnosis of IBS should be considered only if the person has abdominal pain or discomfort that is either relieved by defecation OR associated with altered bowel frequency or stool form. This should be accompanied by at least 2 of the following 4 symptoms:
- Altered stool passage - straining, urgency or incomplete evacuation.
- Bloating, distension, tension, hardness
- Worsened by eating
- Passage of mucus
Rome criteria
Used in secondary care.
Recurrent abdominal pain, on average at least 1 day per week in the last 3 months and associated with two or more of the following criteria:
- Related to defecation
- Associated with a change in frequency of stool
- Associated with a change in form (appearance) of stool
AND
Criteria have been met for the past 3 months and symptoms started at least 6 months prior.
🧰 Management
🥇 This is the first-line management. Conservative management should be followed. Advice should include:
- Sufficient fluids
- Regular, small meals
- Low FODMAP diet - FODMAP stands for fermentable oligosaccharides (wheat, barley, rye), disaccharides (lactose milk, yoghurt, soft cheese), monosaccharides (high fructose fruit and veg, fruit juice, honey) and polyols (artificial sweeteners and some fruits and vegetables). These short-chain carbohydrates cause more symptoms in IBS patients.
- Reduce caffeine, carbonated drinks and alcohol
- Probiotic supplements - if they choose to take then advise them to take it for 12 weeks and if there is no improvement then they should discontinue it.
If IBS-C - advise fibre supplements such as ishpahgula, or oats and linseed.
If IBS-D - reduce insoluble fibre intake (wholemeal, high-fibre flour, bran cereals, brown rice etc.)
🥇 First-line options:
- Antispasmodic - to treat pain caused by abdominal cramps.
- 🥇 Hyoscine butylbromide (buscopan) - a mAChR antagonist that does not cross the BBB and only acts peripherally on the GI tract to prevent spasm.
- Peppermint oil - peppermint has antispasmodic properties due to calcium channel blockade in the gut. It can be taken as a capsule or it may be taken in tea forms.
- Diarrhoea:
- 🥇 Loperamide - u-opioid agonist that decreases peristalsis, enhancing water absorption.
- Constipation:
- 🥇 Bulk-forming laxatives such as isphagula husk.
- ⚠️ In fact any laxative can be considered except for lactulose as this can worsen bloating.
- Linaclotide - is a specialist laxative for those unresponsive to first-line options at max tolerated doses and have had constipation for 12 months.
🥈 Second-line options:
- Low-dose TCA - as stress and PTSD are often causes. A meta-analysis showed that antidepressants aided patients with IBS symptoms.
- Amitryptyline - 5-10mg to be used at night.
🥉 Third-line options:
- SSRIs
- Fluoxetine or citalopram
CBT may be another option to help patients who are unresponsive to pharmacotherapies after 12 months.
Referral to gastroenterology in secondary care is warranted where there is diagnostic doubt, in patients with symptoms that are severe, or refractory to first-line treatments, or where the individual patient requests a specialist opinion.
In those with alarm symptoms or signs, or those with symptoms suggestive of IBS with:
- Diarrhoea who have atypical features and/or relevant risk factors that increase the likelihood of:
- Microscopic colitis (female sex, age ≥50 years
- Coexistent autoimmune disease
- Nocturnal or severe watery, diarrhoea, duration of diarrhoea <12 months,
- Weight loss
- Use of potential precipitating drugs including non-steroidal anti-inflammatory drugs, proton pump inhibitors, etc)