Irritable Bowel Syndrome (IBS), is a condition characterised by a group of symptoms - usually abdominal pain and a change in bowel habit.
Epidemiology
It is thought that around 10-20% of adults in the Western world suffer from IBS symptoms.[i]
Risk Factors and Associations
- Female
- Family History
- History of anxiety, depression, chronic fatigue syndrome, abuse and fibromyalgia
Pathophysiology
The exact pathogenesis of IBS is unknown and there are many proposed theories.
- Psychosocial factors such as pre-existing psychiatric illness can contribute to the development of IBS, but not all patients with have this background.
- A serotonin theory has also been proposed in IBS. Patients with diarrhoea predominant IBS have been shown to have excessive release of serotonin whilst patients with constipation dominant IBS can have serotonin deficiencies.
- Some patients develop IBS following an episode of infective gastroenteritis. There is also evidence that disturbances in the gut microbiota influences development of IBS.
- A brain-gut axis dysregulation theory has also been proposed. There is a connection between the CNS and the enteric nervous system which innervates the GIT – disturbances in the interaction between the two have been proposed as a mechanism behind IBS.[ii]
Clinical Features
- Abdominal pain: Usually cramping/colicky in nature. May be relieved by defecation.
- Change in bowel habits: Can vary between constipation and diarrhoea, and patients will usually have a dominating type e.g. diarrhoea predominant or constipation predominant.
- Passing mucus PR
- Fatigue
- Bloating
- Tenesmus: Feeling of incomplete emptying
- Urgency to open bowels
- Back pain
- Fatigue
- Symptoms worsen with food
Patients are systemically well so unexpected weight loss, vitamin/nutrient deficiencies etc does not occur. Physical examination does not typically elicit any other signs other than abdominal tenderness. [iii]
Differential Diagnosis
- Inflammatory bowel disease
- Colorectal cancer
- Bile salt malabsorption: Chronic diarrhoea, bloating, abdominal pain
- Coeliac disease
- Diverticular disease
Investigations
UK NICE guidelines state that IBS should be considered in patients who have had ABC (abdominal pain, bloating and change in bowel habit) symptoms for at least 6 months.
It is largely a clinical diagnosis, and tends to be a diagnosis of exclusion in that other differentials should be ruled out.
Bloods
- Full blood count: Ensure no anaemia
- ESR and CRP: Ensure no inflammatory process
- Anti-EMA or anti-TTG: Rule out coeliac disease
Stool
- Faecal calprotectin: Rule out Inflammatory bowel disease
- Stool MC&S: Rule out infective causes of diarrhoea
- Faecal occult blood test: Checks for blood in the stool. Is not required in patients who meet IBS criteria but can be considered in diagnostic uncertainty
Special Tests
- Colonoscopy: This can be considered as well but is not required if the presentation is strongly suggestive of IBS
Management
Diet and Lifestyle
- Regular meals
- Reduce intake of caffeinated/alcoholic/fizzy drinks
- Drink enough water
- Fibre may worsen symptoms so reducing intake of fibre may also help.
- Avoiding sorbitol, an artificial sweetener, can also help to reduce diarrhoea.
Anti-Spasmodic Agents
Anti-spasmodic agents can help with pain. Examples include:
- Smooth muscle relaxants: Should not be prescribed in patients with bowel obstruction or ileus.
- Mebeverine hydrochloride
- Alverine citrate
- Hyoscine butylbromide: Common brand name is Buscopan.
- Peppermint oil[iv]
Patients with Diarrhoea
- Antimotility agent: Loperamide is the first line choice
Patients with Constipation
- Patients with constipation predominant IBS can be given laxatives other than lactulose.
- Suitable examples include fybogel and methylcellulose.[v]
- If constipation continues for at least 12 months despite having other laxatives, linaclotide can be used.
Failure of Pharmacological Treatment
- If anti-spasmodic agents and treatment of diarrhoea/constipation with pharmacological methods do not work, tricyclic anti-depressants can be tried at a low dose.
- If this does not work, a selective serotonin reuptake inhibitor can be tried as a third line.
- Additionally, patients who do not respond to pharmacological interventions can be referred for cognitive behavioural therapy or hypnotherapy.
References
[i] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4367204/
[ii] https://atm.amegroups.com/article/view/74950/html
[iii] https://www.nice.org.uk/guidance/cg61/chapter/1-Recommendations#diagnosis-of-ibs
[iv] https://cks.nice.org.uk/topics/irritable-bowel-syndrome/prescribing-information/antispasmodic-drugs/
[v] https://www.nhs.uk/conditions/irritable-bowel-syndrome-ibs/diet-lifestyle-and-medicines/
