Background Information
Definition
IBS is a chronic functional GI disorder, characterised by altered gut-brain interaction.
A functional disorder refers to symptoms occurring in the absence of identifiable structural, biochemical, or inflammatory abnormalities.
Such that, conditions like IBD (Crohn’s and ulcerative colitis), colorectal cancer, coeliac disease etc. are NOT functional disorders, but organic diseases of the GI tract (characterised by structural and/or inflammatory pathology)
Aetiology
The underlying pathophysiology of IBS is not fully understood, likely to be multifactorial. Possible mechanisms:
- Visceral hypersensitivity
- Abnormal GI immune function
- Changes in gut microbiome
- Abnormal autonomic activity
- Abnormal central pain processing of afferent gut signals (altered ‘brain-gut interactions’)
- Abnormal GI motility
Risk factors:
- 20-39 y/o
- Females
- Genetic predisposition
- Dietary factors (e.g. alcohol, caffeine, spicy, fatty foods)
- Psychological comorbidity (e.g. stress, anxiety, depression)
- GI inflammation
- Enteric infection (post-infectious IBS is seen in ~10% patients)
- Drugs like antibiotics
Classification
There are various subtypes of IBS, based on the predominant Bristol stool type:
- IBS with diarrhoea (IBS-D) – most common
- IBS with constipation (IBS-C)
- IBS with mixed bowel habits (IBS-M)
- IBS unclassified (IBS-U) where symptoms meet the criteria for IBS but do not fall into one of the three subgroups above
Diagnosis
IBS is a clinical diagnosis based on:
- Typical clinical features (with NICE criteria / ROME IV criteria), and
- Blood tests to exclude alternative diagnoses
Clinical Features
IBS can be diagnosed clinically, there are no objective tests. The following features are extracted from NICE’s diagnostic criteria, see below for the full diagnostic criteria.
- Core features of IBS (the ABCs):
- Abdominal pain or discomfort that is worsened by eating and relieved by defecation
- Bloating / distension / tension
- Change in bowel habit (bowel frequency or stool form) + passage of mucus
- Other supportive features:
- Lethargy
- Nausea
- Backache
- Bladder symptoms
The follow features suggests an underlying organic pathology, instead of IBS:
- Rectal bleeding / bloody diarrhoea
- Unintentional weight loss
- Nocturnal symptoms
- Fever
- Presence of abdominal / rectal mass
- Family history of IBDInflammatory bowel disease / bowel cancer / ovarian cancer / coeliac disease
Ovarian cancer is an important differential diagnosis to consider, esp. in >50 y/o females with persistent or frequent bloating. As ovarian cancer presents very vaguely, and can mimic IBS.
Full NICE Diagnostic Criteria
- Abdominal pain / discomfort present for at least 6 months, and
- Relieved by defaecation or associated with altered bowel frequency (increased or decreased)or stool form (hard, lumpy loose, or watery), and
- At least 2 of the following
- Altered stool passage (straining, urgency, incomplete evacuation)
- Abdominal bloating (more common in women than men), distension, tension or hardness
- Symptoms made worse by eating
- Passage of mucus
Other features such as lethargy, nausea, backache and bladder symptoms are common in people with IBS, and may be used to support the diagnosis
NICE CKS states that ROME IV Criteria for IBS are often used in secondary care (which is very similar to those recommended by NICE).
Work-Up
The following tests should be performed routinely in those who meet the IBS clinical diagnostic criteria:
- FBC
- ESR and CRP
- Coeliac serology
- Faecal calprotectin – esp. in those ≤45 y/o (advised by NICE CKS, to exclude inflammatory bowel disease)
IBS typically has normal routine blood tests as it is a functional bowel disorder without underlying inflammation
- FBC → no anaemia, normal white cell count
- ESR and CRP → not elevated (if elevated, consider IBD or infection)
- Coeliac serology → -ve IgA tTG
- Faecal calprotectin → not elevated (if elevated, suggest IBD)
Colonoscopy is NOT routinely indicated. It is reserved for patients with red-flag features suggestive of colorectal malignancy or for those who meet criteria for national bowel cancer screening.
Management
Conservative / General Management
Advise the following:
- Regular meals and take time to eat (avoid missing meals or leaving long gaps between meals)
- At least 8 cups of fluid per day (esp. water or non-caffeinated drinks)
- Oats and linseeds may be helpful for wind and bloating
- These are soluble fibres, insoluble fibres should be discouraged
- 2nd line: consider exclusion diets – e.g. FODMAPFermentable oligosaccharides, disaccharides, monosaccharides and polyols diet (only to be started by those with expertise in dietary management)
The following should be AVOIDED or RESTRICTED (as they may worsen symptoms):
- Tea and coffee (to max 3 cups per day)
- Alcohol and fizzy drinks
- High-fibre food (insoluble fibres, e.g. wholemeal or high‑fibre flour and breads, cereals high in bran, and whole grains such as brown rice)
- Fresh fruit (to max 3 portions per day)
- Sorbitol (an artificial sweetener) – avoid in those who experience diarrhoea
- Resistant starch (often found in processed or re-cooked foods)
Pharmacological Management
Management depends on the predominant symptom:
| Predominant symptom | Treatment |
|---|---|
| Constipation |
|
| Diarrhoea |
|
| Abdominal pain / spasm |
|
References
NICE guideline Irritable bowel syndrome in adults: diagnosis and management
NICE CKS Irritable bowel syndrome