What is Irritable Bowel Syndrome (IBS)?

Understanding Irritable Bowel Syndrome (IBS)

Irritable Bowel Syndrome (IBS) is a chronic functional gastrointestinal disorder characterized by recurrent abdominal pain associated with altered bowel habits that cannot be explained by structural or biochemical abnormalities. 1

Definition and Diagnostic Criteria

IBS is diagnosed using the Rome III criteria, which require:

• Recurrent abdominal pain or discomfort for at least 3 days per month in the last 3 months, associated with two or more of the following:
  • Improvement with defecation
  • Onset associated with change in stool frequency
  • Onset associated with change in stool form/appearance 1

These symptoms should be present for at least 6 months prior to diagnosis to be considered chronic.

Epidemiology

IBS is extremely common worldwide:

• Prevalence ranges from 2.5% to 25% depending on the criteria used and population studied
• More common in women than men
• Typically affects people under 50 years of age
• Prevalence varies by country (e.g., 14.1% in USA, 6.6% in Hong Kong, 8.5% in Italy) 1

IBS Subtypes

Based on predominant stool consistency, IBS is classified into:

1. IBS with constipation (IBS-C): Hard stools >25% of the time and loose stools <25% of the time
2. IBS with diarrhea (IBS-D): Loose stools >25% of the time and hard stools <25% of the time
3. IBS with mixed bowel habits (IBS-M): Both hard and soft stools >25% of the time
4. Unclassified IBS (IBS-U): Neither loose nor hard stools >25% of the time 1

Some patients switch between subtypes over time and are termed "alternators."

Clinical Features

Key Symptoms

• Abdominal pain: Central feature, often relieved by defecation
• Altered bowel habits: Constipation, diarrhea, or alternating patterns
• Bloating: Common and often distressing
• Additional symptoms:
  • Mucus in stool
  • Feeling of incomplete evacuation
  • Urgency
  • Straining during defecation 1

Symptom Patterns

• Most patients experience intermittent symptoms with flares lasting 2-4 days followed by remission
• Morning symptoms are common, with repeated defecation and progressive loosening of stool
• Symptoms often worsen after meals and during periods of stress 1

Pathophysiology

Multiple mechanisms contribute to IBS development:

1. Brain-gut axis dysregulation: Altered communication between central nervous system and enteric nervous system 1
2. Visceral hypersensitivity: Increased pain perception to normal gut stimuli 1, 2
3. Altered gut motility: Abnormal contractions affecting transit time 1
4. Low-grade inflammation: Particularly in post-infectious IBS 3
5. Altered gut microbiota: Dysbiosis may contribute to symptoms 4
6. Psychological factors: Stress, anxiety, and depression can trigger or worsen symptoms 1

Diagnosis

Diagnosis is based on:

1. Positive symptom criteria (Rome III criteria)

2. Absence of alarm features:

   • Age >50 years
   • Weight loss
   • Rectal bleeding
   • Nocturnal symptoms
   • Family history of colon cancer
   • Anemia 1

3. Helpful diagnostic behavioral features:

   • Symptoms present >6 months
   • Frequent consultations for non-GI symptoms
   • Previous medically unexplained symptoms
   • Patient reports stress aggravates symptoms 1

Limited investigations are needed in typical cases without alarm features.

Management Approach

Management requires a multidisciplinary approach addressing:

1. Medical Management

• Antispasmodics: For pain and cramping
• Laxatives: For constipation-predominant IBS
• Antidiarrheals: For diarrhea-predominant IBS
• 5-HT3 receptor antagonists (e.g., alosetron): For IBS-D, works by modulating enteric nervous system 5, 6
• GC-C agonists: For IBS-C
• Antibiotics (e.g., rifaximin): For IBS with bloating 6, 3
• Antidepressants: Particularly useful when psychological comorbidities exist 6

2. Dietary Modifications

• Identify and avoid trigger foods
• Consider dietary approaches (low FODMAP diet)
• Ensure adequate fiber intake, particularly for IBS-C 1

3. Psychological Therapies

• Cognitive behavioral therapy
• Stress management techniques
• Relaxation training 1, 6

Impact on Quality of Life

IBS significantly impacts quality of life:

• Impairs physical, emotional, and social functioning
• Causes work absenteeism
• Creates substantial healthcare costs
• Often associated with anxiety and depression 1

Prognosis

• Chronic condition with waxing and waning symptoms
• Poor prognostic factors include:
  • Long history of symptoms
  • Ongoing life stressors
  • Psychological comorbidities 1
• Not associated with development of serious disease or excess mortality

IBS requires long-term management strategies focusing on symptom control and improving quality of life rather than cure.