Gastroenterology & Family Medicine & Psychosomatics
Irritable bowel syndrome (IBS)
Irritable bowel syndrome (IBS) — also known in English as Irritable Bowel Syndrome (IBS) — is the most common functional bowel disorder, defined as a disorder of gut-brain interaction (DGBI — Disorder of Gut-Brain Interaction, formerly known as functional gastrointestinal disorder) characterized by chronic, recurrent abdominal pain associated with changes in bowel habits (diarrhea, constipation, or alternating), in the absence of identifiable structural or biochemical organic lesions. With a global prevalence of 10 to 15% of the adult population—including approximately 1.5 to 2 million Quebecers — IBS is the most commonly diagnosed gastrointestinal condition in primary care after gastroesophageal reflux disease, accounting for 30 to 50% of gastroenterology consultations and an economic burden (absenteeism, consultations, and tests) estimated at billions of dollars annually in North America. Its pathophysiology is multifactorial and complex, involving a disrupted bidirectional interaction between the enteric nervous system (abdominal brain + 500 million neurons) and the central nervous system (brain-gut axis) → visceral hypersensitivity (lowered pain threshold to normal intestinal stimuli) + abnormal intestinal motility + gut microbiome dysbiosis + increased intestinal permeability (leaky gut) + low-grade mucosal inflammation + psychosocial factors (anxiety + depression + history of trauma + stressful life events). Acute infectious gastroenteritis precedes IBS in 10 to 20% of cases (post-infectious IBS)—a mechanism that is particularly important to document, as these forms may benefit from rifaximin. The diagnosis is made according to the Rome IV criteria (2016)—internationally validated positive clinical criteria—without requiring extensive additional testing in the absence of red flags, thereby avoiding a costly and anxiety-inducing diagnostic cascade for a functional disorder with a benign prognosis.
Rome IV Criteria (2016) — Positive Diagnosis
- Core criterion: Recurrent abdominal pain ≥ 1 day per week on average during the last 3 months + symptoms present for ≥ 6 months
- Associated with ≥ 2 of the following 3 criteria: Bowel movement relationship (pain improves or worsens with bowel movement) + change in stool frequency + change in stool form (according to Bristol Stool Scale)
- Subtypes (Rome IV classification): IBS-D (predominantly diarrhea — more than 25% of stools are Bristol type 6–7) + IBS-C (predominantly constipation — more than 25% of stools are Bristol type 1–2) + IBS-M (mixed — alternating diarrhea and constipation) + IBS-U (unclassifiable)
- MS is a positive diagnosis (not a diagnosis of exclusion): In the absence of red flags → no need for colonoscopy + no need for CT scan + no need for exhaustive workup → diagnosis relies on Rome IV clinical criteria + a normal physical examination + a normal basic biological workup (CBC + CRP + TSH + creatinine + ferritin + anti-transglutaminase IgA antibodies if gluten intolerance is suspected)
Red flags — indications for further investigation
- Rectal bleeding or blood in the stool
- Unintentional weight loss > 5–10% of body weight
- Unexplained anemia (iron deficiency or otherwise)
- Nocturnal symptoms awakening the patient (nocturnal diarrhea)
- Fever + abdominal pain
- Onset of symptoms after age 50
- Family history of colorectal cancer + Crohn's disease + ulcerative colitis + celiac disease
- Biological anomalies: elevated CRP + elevated fecal calprotectin (> 50 µg/g) + anemia + hypoalbuminemia
- In the presence of one or more red flags: Colonoscopy OR abdominal CT scan OR gastroscopy as indicated → Exclude colorectal cancer, IBD, celiac disease, chronic infections
Pathophysiology — Brain-Gut Axis
- Visceral hypersensitivity lowered pain threshold in the colon → normal gas distension felt as painful → visceral allodynia → central mechanism via sensitization of intestinal nociceptive afferent pathways
- Microbiome dysbiosis alteration of gut flora composition → excessive fermentation of FODMAPs → production of hydrogen + methane + CO₂ → distension + bloating + pain + abnormal motility
- Post-infectious SCI Following acute gastroenteritis → persistent inflammation of the mucosa + increased intestinal permeability + changes in the microbiome → IBS in 10–20% of cases → risk factors: female gender + psychological stress during the infectious episode + duration of the infection + severity
- Psychosocial factors: anxiety + depression (comorbidities in 50–90% of moderate-to-severe cases) + history of physical or sexual abuse + post-traumatic stress disorder → the brain-gut axis is bidirectional: stress increases intestinal permeability + motility + visceral sensitivity
Treatment — Phased Approach
| Approach | Treatment | Subtype + efficacy |
|---|---|---|
| General measures (all subtypes) | Education + psychoeducation (reassurance about the absence of serious injury) + identification of triggering factors (stress + foods + sleep regularity) + regular physical activity (30 min x 5/week) + symptom journal | Reassurance and education reduce symptom-related anxiety, exercise improves bowel motility, mood, and quality of life in all subtypes. |
| Low FODMAP diet | Strict reduction of Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols for 4–8 weeks → gradual reintroduction phase to identify specific trigger foods + supervised by a specialized dietitian | Effective in 50–70% of patients (Cochrane meta-analyses) + IBS-D and IBS-M ++ + improvement seen in all subtypes + FODMAPs to avoid: wheat + rye + onions + garlic + milk + legumes + apples + pears + certain sweeteners |
| Antispasmodics (pain + bloating) | Dicyclomine hydrochloride (Bentylol®) 20 mg four times daily or mebeverine 135 mg three times daily or hyoscine butylbromide (Buscopan®) or peppermint oil (Colpermin® - enteric 0.2 mL three times daily) - intestinal smooth muscle relaxant | Moderate effectiveness on pain and cramps + peppermint oil = as effective as chemical antispasmodics + fewer anticholinergic side effects + better tolerance |
| IBS-D (diarrhea-predominant) | Loperamide (Imodium®) 2 mg after each loose stool (max 16 mg/day) + rifaximin 550 mg three times a day for 14 days (non-absorbable antibiotic - IBS-D + post-infectious IBS) + cholestyramine if bile acid diarrhea (post-cholecystectomy) + eluxadoline (enteric opioid) + ondansetron 4 mg (refractory IBS-D) | Rifaximin: 40–60% remission at 4 weeks + sustained effect for 6–12 weeks + addresses dysbiosis + loperamide: reduces stool frequency and post-bowel movement cramps + does not treat pain |
| IBS-C (constipation-predominant) | Soluble fiber (psyllium Metamucil® 15 g/day) + polyethylene glycol (PEG — Lax-A-Day®) + linaclotide 290 µg/day (GC-C agonist → intestinal secretion + transit — Health Canada approved IBS-C) + prucalopride (selective 5-HT4 prokinetic) | Soluble fiber (psyllium): modest symptom reduction + well-tolerated + linaclotide: better efficacy on abdominal pain AND constipation (LIBER + LEED trials) + prucalopride: effective on colonic transit |
| Antidepressants (neuropathic pain + comorbidities) | Low-dose tricyclics (amitriptyline 10–50 mg at bedtime) → central visceral analgesia + slow transit (IBS-D++) + SSRIs (fluoxetine + sertraline) → speed up transit + anxiety + depression (IBS-C or forms with an anxious component++) | Tricyclics: Significant reduction in visceral pain and stool frequency in IBS-D (meta-analyses) + pain relief doses (non-antidepressant) → explain to patient + SSRIs: less effective on digestive symptoms than tricyclics + but better tolerated |
| Psychological therapies | CBT (Cognitive Behavioral Therapy) + Gut-Directed Hypnotherapy + Mindfulness + Psychodynamic Psychotherapy | TCC and gut hypnotherapy: significant reduction in digestive symptoms AND quality of life (Cochrane meta-analyses) + comparable efficacy to pharmacological treatments in forms with psychiatric comorbidities + to be systematically recommended in moderate to severe forms |
ℙ️
Fecal calprotectin is an inflammatory marker of the intestinal mucosa released by neutrophils—it is elevated in IBD (UC and Crohn’s disease) and normal in IBS. A level < 50 µg/g has a negative predictive value of over 95% for ruling out active IBD—making it an excellent screening tool for avoiding unnecessary colonoscopy in typical IBS. It is particularly useful for distinguishing an IBD flare-up from post-inflammatory IBS in a patient with a known IBD diagnosis.
Medical consultation recommended
Consult a doctor if chronic abdominal pain and bowel habit disorders persist and affect quality of life. An accurate diagnosis according to Rome IV criteria and a basic biological assessment (CBC, CRP, fecal calprotectin, celiac antibodies) will help rule out an organic cause and initiate appropriate treatment for the subtype. Consult quickly if rectal bleeding, weight loss, anemia, fever, or nighttime diarrhea accompany the symptoms - these red flags warrant a colonoscopy. For an IBS diagnosis, initiation of the FODMAP diet, antispasmodics, or linaclotide, Clinique Omicron offers medical consultations at its service points in Quebec and via telemedicine. To make an appointment, visit cliniqueomicron.ca.
Consult at Clinique Omicron
Clinique Omicron's doctors and nurse practitioners (NPs) diagnose IBS according to Rome IV criteria, look for red flags that warrant further investigation, prescribe fecal calprotectin to distinguish IBS from IBD, initiate treatment tailored to the subtype (FODMAP + antispasmodics + loperamide + linaclotide + rifaximin + amitriptyline), refer to dietitians for FODMAP diet support, recommend psychological therapies (CBT + gut-directed hypnotherapy) for severe forms, and refer to gastroenterology for complex cases or those requiring a colonoscopy. Consultations are available at several service points in Quebec and via telemedicine. To book an appointment, visit cliniqueomicron.ca.
The content of this page is for informational purposes only and does not substitute for the advice of a doctor or gastroenterologist. IBS is a positive clinical diagnosis according to Rome IV criteria—a colonoscopy is not necessary in the absence of red flags in patients under 50 years old. The FODMAP diet should be supervised by a specialized dietitian to be effective and not lead to nutritional deficiencies.
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