Irritable Bowel Syndrome

i.e. in exam question land- a young woman, who is probably a lawyer, is stressed at work and comes to the GP complaining of diarrhoea.

Irritable Bowel Syndrome (IBS)

Definition: a chronic mixed group of abdominal symptoms for which no organic cause can be found.

Several diagnostic criteria exist that evaluate symptoms and their duration e.g. Manning, Rome.

Aetiology/ risk factors:

-Unknown cause

-Visceral sensory abnormalities, gut motility abnormalities, psychosocial factors (particularly stress), food intolerance (e.g. lactose) are all implicated

-Stress or depression is seen in ≥ 50%

Epidemiology: Prevalence = 10-20%

Age at onset 40 years

> 2x more common in females


For diagnosis

Abdominal pain/ discomfort (often colicky, in lower abdomen)

      -that may be relieved by defecation OR

      -that may be associated with altered stool form or bowel frequency

                  –Constipation and diarrhoea may alternate

And 2+ of


Incomplete evacuation

-Abdominal bloating/distension

-PR mucus

Worsening of symptoms after food

-Other: Nausea, bladder symptoms, backache

Symptoms are chronic (>6M) and exacerbated by stress, menstruation, or gastroenteritis (post-infection IBS)

Screen for red flag features, which would prompt referral to exclude colon cancer: weight loss, anaemia, PR bleeding, late onset (> 60).


-Examination often normal

-General abdominal tenderness common

-Distended/bloated abdomen

⇒Things that would point towards alternative diagnosis: > 40 years old (esp Male), < 6M history, anorexia, weight loss, waking up at night with pain/diarrhoea, mouth ulcers, abnormal CRP, ESR, Hb, coeliac serology.


No specific investigations for IBS but need to do relevant investigations to rule out other differential causes of symptoms, such as UC, Crohn’s, infectious colitis, coeliac disease:

-Bloods- FBC (anaemia?), ESR, CRP, LFTs, Coeliac Serology are enough if the history is classic.

Colonoscopy (will be normal if IBS):

-If  50yrs or any marker of organic disease e.g. fever, PR bleed, weight loss

-If family history of ovarian (serum marker CA-125 to help exclude) or bowel cancer have lower threshold

-If diarrhoea prominent:


Stool culture (for parasites, cysts and infection)


Anti-endomysial antibodies (coeliac disease)

TSH (hyperthyroidism)

-Consider barium follow-through (if symptoms suggest small bowel disease) +/- rectal biopsy

-Further investigations, guided by symptoms:

Upper GI endoscopy (reflux, dyspepsia)

Small bowel radiology (Crohn’s)

Duodenal biopsy (Coeliac disease)

Giardia tests (parasite that often triggers IBS)

ERCP/MRCP (pancreatitis)

Ultrasound (gallstones)


Refer if:

-Diagnosis unsure

-Changing symptoms in ‘known IBS’

-Rectal mucosal prolapse ⇒⇒surgeon

-Food intolerance ⇒⇒ dietician

-Stress or depression or refractory symptoms ⇒⇒ hypnotherapist or psychotherapist

-Cyclical pain, dyspareunia, dysmenorrhoea, raised Ca-125, endometriosis often mimics IBS ⇒⇒ gynaecologist

-Co-existing atopy- IBS 3x more common in atopy ⇒⇒ dermatologist

-Chronic pain overlap syndromes (fibromyalgia + chronic fatigue + chronic pelvic pain) or detrusor problems ⇒⇒Pain clinic

-Ensure a healthy diet. Fibre, lactose, fructose, wheat, starch, caffeine, sorbitol, alcohol and fizzy drinks may worsen symptoms. Probiotics and water-soluble fibre may be ok.

     –FODMAP = “Fermentable, Oligo-, Di- (lactose), Mono-saccharides (fructose) And Polyols (sorbitol). FODMAP restriction has been found to improve symptom control in people with IBS.

Image result for fodmap

Depending on predominating symptoms

Constipation      Bisacodyl and sodium picosulfate can help.

Ispaghula has non-fermentable water-soluble fibre (better than lactulose which ferments, exacerbating bloating)

Increasing fibre is not a good solution as it can worsen flatulence/bloating, so insoluble fibre should be avoided.

Diarrhoea           Avoid sorbitol sweeteners

Bulking agent +/- loperamide (2mg after each loose stool, max 16mg/d)

Colic/bloating     Oral antispasmodics: mebeverine, alverine citrate, dicycloverine

Adding Simeticone improves spasm (anti-foaming agent)

Probiotic strains: Bacillus coagulans GBI-30, B.infantis 35624, E.coli DSM17252, L.acidophilus

Psychological symptoms

Cognitive behavioural therapy (CBT)


Tricyclics e.g. amitriptyline


-physical and psychological morbidity

-increased incidence of colonic diverticulosis

Prognosis: in 50% symptoms go or improve after 1 year. Less than 5% worsen.

References: Cheese & Onion, Rapid Medicine

3 thoughts on “Irritable Bowel Syndrome

  1. Jackie says:

    I did a cheer when I saw the FODMAP diet included here. Older doctors aren’t typically familiar with it and (understandably) assume it’s a new age diet when I mention it – not the science based diet it actually is.

    Liked by 1 person

    • clumsylostmedicalstudent says:

      We had a dietician give us a lecture on diet and bowel diseases last year, and she mentioned the FODMAP diet, though it isn’t actually in my reference texts. So that’s a whole lot of medical students that now know about FODMAP- unless they weren’t paying attention… 🙂

      Liked by 1 person

      • Jackie says:

        This may have been mentioned, but there’s an excellent (but a bit pricey – $8) app put out by Monash University to help guide patients. It uses a traffic light system on which foods are safe, and at what quantities. The foods are primarily whole foods, but I still found it helpful when first starting. Monash is constantly testing additional foods and updating the app.

        Liked by 1 person

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