Diagnostic Criteria and Treatment Options for Irritable Bowel Syndrome (IBS)
Diagnostic Criteria
IBS should be diagnosed using the Rome III/IV Criteria, which requires recurrent abdominal pain at least 1 day per week in the last 3 months (with symptoms present for at least 6 months), associated with at least 2 of the following: pain relieved by defecation, onset associated with change in stool frequency, or onset associated with change in stool form/consistency. 1
Supporting symptoms include:
- Abnormal stool frequency
- Abnormal stool form
- Abnormal stool passage
- Passage of mucus
- Bloating or feeling of abdominal distention 1
IBS Subtypes
IBS is classified into subtypes based on predominant stool patterns:
| Subtype | Characteristics |
|---|---|
| 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) | Mixed stool pattern |
| IBS-U (unclassified) | Does not fit other categories |
Diagnostic Approach by Age
- Patients ≤50 years with typical symptoms and no alarm features: Can be diagnosed confidently based on Rome criteria with limited or no additional testing 1
- Patients >50 years: Should undergo colonoscopy due to higher risk of colorectal cancer 1
Red Flags Requiring Further Investigation
- Age >50 years at symptom onset
- Short history of symptoms
- Documented weight loss
- Nocturnal symptoms
- Family history of colorectal cancer or IBD
- Anemia
- Rectal bleeding
- Recent antibiotic use 1
Recommended Laboratory Testing
Basic Testing for All Patients
- Complete blood count
- Stool Hemoccult test
- Consider ESR/CRP (especially in younger patients)
- Serum chemistries and albumin
- Celiac disease screening 1
Subtype-Specific Testing
IBS-D:
- Stool for ova and parasites in endemic areas
- Lactose/dextrose H2 breath test if lactose intolerance suspected
- Colonoscopy with biopsies to rule out microscopic colitis in patients with risk factors 1
IBS-C:
- Initial therapeutic trial of fiber
- For persistent symptoms: consider transit studies or defecography 1
Treatment Options
General Approach
- Provide clear explanation that IBS is a disorder of gut-brain interaction
- Reassure patients about benign prognosis (not associated with increased mortality or cancer risk)
- Address psychosocial factors that may affect symptoms
- Target treatment to predominant symptoms 1
Pharmacologic Treatment by Subtype
IBS-C (Constipation-predominant)
- First-line: Osmotic laxatives
- Second-line: Stimulant laxatives
- Additional options: Antispasmodics, neuromodulators, secretagogues 1
- Important: Don't use only laxatives without addressing the pain component 1
IBS-D (Diarrhea-predominant)
- First-line: Anti-diarrheal drugs
- Second-line: 5-HT3 antagonists, eluxadoline, or rifaximin (where available) 2
For Abdominal Pain (All Subtypes)
- First-line: Antispasmodics
- Dicyclomine has shown 82% favorable clinical response compared to 55% with placebo in controlled trials 3
- Second-line: Gut-brain neuromodulators (low-dose tricyclic antidepressants like amitriptyline preferred) 2
Non-Pharmacologic Approaches
- Traditional dietary advice as first-line approach
- Consider specialist dietetic guidance if response is incomplete
- Probiotics may be beneficial (though evidence quality is limited) 2
- Brain-gut behavioral therapies (effective for patients refractory to standard therapies) 2
- Lifestyle modifications: stress reduction, physical activity 1
Common Pitfalls to Avoid
- Excessive investigation in patients with typical symptoms and no alarm features
- Treating IBS-C with only laxatives without addressing pain
- Ignoring psychosocial factors that significantly affect symptoms and treatment outcomes
- Failing to address comorbidities like fibromyalgia, anxiety, and depression 1
- Overlooking the need for colonoscopy in patients >50 years 1
Recent research suggests that relaxing the frequency requirement for abdominal pain to 3 days per month (rather than 1 day per week) may improve diagnostic performance 4, but the American Gastroenterological Association still recommends the standard Rome criteria for diagnosis 1.