What is Irritable Bowel Syndrome (IBS)?

What is Irritable Bowel Syndrome (IBS)?

IBS is a common disorder of gut-brain interaction affecting 5-10% of the global population, characterized by recurrent abdominal pain associated with altered bowel habits (diarrhea and/or constipation) and often bloating, diagnosed based on positive symptom criteria rather than structural abnormalities. 1

Core Definition and Epidemiology

IBS is a functional gastrointestinal disorder where individuals experience chronic symptoms without identifiable structural or biochemical abnormalities. 1 The condition affects 4-10% of the population globally, with prevalence estimates ranging from 9-23% depending on the population studied. 2, 3 The condition is more common in women, with approximately 80% of patients being female. 4

Diagnostic Criteria

Diagnosis requires recurrent abdominal pain occurring at least 3-4 days per month for the past 3 months, with symptom onset at least 6 months prior to diagnosis. 5, 6 The pain must be associated with two or more of the following features: 1

• Relief with defecation
• Onset associated with a change in stool frequency
• Onset associated with a change in stool form or appearance

The fundamental distinction from other bowel disorders is that the abdominal pain must be clearly linked to bowel function—this is what separates IBS from chronic idiopathic constipation (CIC), which presents as painless constipation. 7

Clinical Subtypes

IBS presents in three predominant patterns based on stool consistency: 1, 3

• IBS with constipation (IBS-C): Hard or lumpy stools ≥25% of the time and loose/watery stools <25% of the time 6
• IBS with diarrhea (IBS-D): Loose or watery stools ≥25% of the time and hard/lumpy stools <25% of the time 6
• Mixed IBS (IBS-M): Both hard and loose stools occurring ≥25% of the time 2

Pathophysiology

The symptoms have a physiological basis involving three interrelated mechanisms: 1

1. Altered gut reactivity: Abnormal motility and secretion in response to meals, gut distention, inflammation, bacterial factors, or psychosocial stress, resulting in diarrhea and/or constipation 1
2. Visceral hypersensitivity: Enhanced perception of gut sensations and pain 1
3. Brain-gut axis dysregulation: Altered stress reactivity and abnormal processing of visceral signals 1

Additional emerging mechanisms include post-infectious low-grade inflammation, altered gut microbiota, genetic and immunologic factors, and dietary triggers. 8

Associated Features and Impact

Supportive symptoms that strengthen the diagnosis include: 1

• Abnormal stool frequency (>3 bowel movements per day or <3 per week)
• Abnormal stool form
• Straining, urgency, or incomplete evacuation
• Passage of mucus
• Bloating or abdominal distention

Up to one-third of people with IBS experience comorbid anxiety or depression, which significantly impacts quality of life more than the gastrointestinal symptoms alone. 1 The condition causes substantial work impairment, with 5-50% of patients requiring time off work and 82% experiencing overall work impairment. 1

Diagnostic Approach

Diagnosis is based on positive symptom identification using Rome criteria, not exclusion of all possible organic diseases. 1 Initial workup should screen for alarm features including: 5

• Age >50 years
• Documented weight loss
• Nocturnal symptoms
• Rectal bleeding
• Anemia
• Fever
• Family history of colon cancer or inflammatory bowel disease

Baseline investigations should include complete blood count, inflammatory markers (C-reactive protein or ESR), celiac serology, and fecal calprotectin. 5 In the absence of red flags, extensive diagnostic testing is not recommended and increases healthcare costs without improving outcomes. 6

Management Framework

An integrated care model addressing gastrointestinal symptoms with medical management, dietary modifications, and brain-gut behavioral therapies delivered by a multidisciplinary team is considered the gold standard. 1 This approach should empower patients to self-manage their condition over time. 1

The condition is chronic and requires understanding that no single etiological mechanism explains all symptoms—treatment must be tailored to the predominant symptom pattern and individual patient factors. 8