What is the appropriate diagnostic and treatment approach for a patient presenting with symptoms consistent with Irritable Bowel Syndrome (IBS)?

IBS Diagnosis and Management

Making the Diagnosis

IBS should be diagnosed as a positive, symptom-based diagnosis—not a diagnosis of exclusion—when patients meet Rome IV criteria and lack alarm features. 1

Core Diagnostic Criteria

The diagnosis requires recurrent abdominal pain at least 1 day per week in the last 3 months, associated with two or more of the following: 1

• Pain relieved by defecation
• Pain associated with change in stool frequency
• Pain associated with change in stool consistency

Symptoms must have onset at least 6 months prior to diagnosis. 1

Essential History Elements

Cardinal symptoms to confirm: 1

• Relationship between abdominal pain and bowel habit changes (this is the defining feature)
• Stool pattern using Bristol stool chart on days when stools are abnormal
• Presence of bloating (highly suggestive when present, though not required)

Additional supportive features that strengthen the diagnosis: 1

• Female sex, age <45 years
• Symptom duration >2 years
• Frequent past consultations for non-gastrointestinal symptoms
• Patient reports stress aggravates symptoms
• Extraintestinal symptoms: back pain, urological symptoms, gynecological symptoms, fibromyalgia, tension headache, chronic fatigue
• History of postinfectious onset, recurrent antibiotic use, or acute/chronic stress

Alarm Features Requiring Further Investigation

Immediately refer for colonoscopy or imaging if any of these are present: 1

• Age >50 years with new onset symptoms
• Unintentional weight loss
• Rectal bleeding or bloody diarrhea
• Nocturnal diarrhea or abdominal pain
• Anemia
• Family history of colon cancer or inflammatory bowel disease
• Short symptom duration (<6 months)
• Recent antibiotic use (raises concern for infection)

Baseline Investigations

Required for all patients in primary care or at first secondary care appointment: 1

• Full blood count
• C-reactive protein or erythrocyte sedimentation rate
• Coeliac serology
• Faecal calprotectin (if diarrhea present AND age <45 years)

Interpreting Faecal Calprotectin

1

• If ≥250 μg/g: High suspicion for IBD, proceed directly to colonoscopy
• If 100-249 μg/g: Repeat test off NSAIDs and proton pump inhibitors; refer for colonoscopy if remains elevated
• If normal: Proceed with IBS diagnosis

When to Consider Additional Testing

For IBS-D with atypical features (nocturnal diarrhea, prior cholecystectomy): 1

• SeHCAT scanning or serum 7α-hydroxy-4-cholesten-3-one to exclude bile acid diarrhea
• Between 25-33% of suspected IBS-D patients have abnormal bile acid retention
• Response to bile acid sequestrants is higher with retention <10% or <5%

For IBS-D to exclude microscopic colitis, consider colonoscopy with biopsies if: 1

• Female sex
• Age ≥50 years
• Coexistent autoimmune disease
• Nocturnal or severe watery diarrhea
• Duration of diarrhea <12 months
• Weight loss
• Use of NSAIDs, PPIs, SSRIs, or statins

Colonoscopy has extremely low yield otherwise and provides no reassurance benefit to patients. 1

Subtype Classification

Based solely on stool consistency using Bristol stool chart: 1

• IBS-C (constipation): Hard stools >25% of the time AND loose stools <25% of the time
• IBS-D (diarrhea): Loose stools >25% of the time AND hard stools <25% of the time
• IBS-M (mixed): Both hard and loose stools >25% of the time
• IBS-U (unclassified): Neither loose nor hard stools >25% of the time

Communicating the Diagnosis

After completing the clinical assessment, confidently communicate a positive diagnosis of IBS based on symptoms. 1

Key Educational Points to Convey

1

• IBS is a disorder of gut-brain interaction involving visceral hypersensitivity
• It is a chronic condition with fluctuating symptoms triggered by stress, illness, drugs, and eating
• IBS does not increase risk of cancer or mortality
• Quality of life impairment equals that of organic diseases like IBD
• Cure is unlikely, but substantial improvement in symptoms and quality of life is achievable
• Treatment targets the gut-brain axis through dietary, pharmacological, and psychological approaches

Initial Treatment Approach

First-Line Management for All Patients

Lifestyle modifications: 2

• Regular physical exercise (benefits last up to 5 years)
• Establish regular times for defecation
• Implement proper sleep hygiene

Dietary interventions: 2

• Provide standard first-line dietary advice
• Start soluble fiber supplementation (ispaghula 3-4g/day, gradually increase)
• Avoid insoluble fiber (wheat bran) as it may worsen symptoms
• Consider low FODMAP diet as second-line under dietitian supervision

Symptom-Directed Pharmacotherapy

For IBS-D (diarrhea-predominant): 1, 2

• First-line: Loperamide 2-4 mg up to four times daily, carefully titrated
• Second-line: Rifaximin 550 mg three times daily for 14 days (47% response rate vs 39% placebo for combined pain and stool improvement)
• Alternatives: Ondansetron or ramosetron

For IBS-C (constipation-predominant): 1

• Increase dietary fiber to 25 g/day
• Osmotic laxatives if fiber insufficient

For abdominal pain: 1, 2

• First-line: Antispasmodics (anticholinergics) or peppermint oil, particularly when meal-related
• Second-line: Low-dose tricyclic antidepressants if antispasmodics fail (provides dual benefit for pain and sleep)

For IBS-M (mixed type): 2

• Antispasmodics for pain relief
• SSRIs for global symptom improvement
• Consider psychological therapy early

Severe IBS-D: Alosetron Considerations

Alosetron is indicated ONLY for women with severe diarrhea-predominant IBS who have: 3

• Chronic symptoms (≥6 months duration)
• Excluded anatomic/biochemical GI abnormalities
• Failed conventional therapy
• Severe IBS defined as diarrhea PLUS ≥1 of: frequent/severe abdominal pain, frequent urgency/fecal incontinence, or disability restricting daily activities

Dosing: 3

• Start 0.5 mg twice daily
• May increase to 1 mg twice daily after 4 weeks if well-tolerated but inadequate control
• Discontinue if no adequate control after 4 weeks at 1 mg twice daily

Critical safety warnings: 3

• Contraindicated if constipation present at baseline, history of chronic/severe constipation, ischemic colitis, impaired intestinal circulation, severe hepatic impairment, or concomitant fluvoxamine use
• Discontinue immediately if constipation develops (29% incidence at 1 mg twice daily)
• Discontinue immediately if signs of ischemic colitis occur (rectal bleeding, bloody diarrhea, new/worsening abdominal pain)
• Serious complications include obstruction, ileus, impaction, toxic megacolon, perforation, and death
• Risk increased in elderly, debilitated patients, or those on medications decreasing bowel motility

Psychological Interventions

Consider early in treatment algorithm, particularly with psychological comorbidity: 2

• Cognitive behavioral therapy
• Gut-directed hypnotherapy
• Mindfulness-based stress reduction
• Brain-gut behavioral therapies improve quality of life by 32-39% compared to controls

For frequent or severe pain, or comorbid depression/anxiety: 1, 2

• Tricyclic antidepressants at low doses
• SSRIs at therapeutic doses for those with established mood disorders

Follow-Up and Monitoring

Reassess after 4-6 weeks of initial treatment: 2

• Evaluate both gastrointestinal and psychological symptoms
• Adjust treatment based on symptom evolution
• If no improvement with first-line therapies, consider testing for specific dysfunctions (rectal evacuation disorder, abnormal colonic transit, bile acid diarrhea)

Common Pitfalls to Avoid

1, 2

• Treating IBS as diagnosis of exclusion rather than positive symptom-based diagnosis
• Ordering colonoscopy in patients without alarm features (provides no benefit)
• Focusing only on GI symptoms while neglecting psychological factors
• Overreliance on medications without addressing lifestyle and dietary factors
• Implementing restrictive diets without proper dietitian supervision
• Using low-dose TCAs as monotherapy in patients with established mood disorders
• Failing to recognize that up to 80% of IBS patients report at least one alarm symptom (modest diagnostic performance)