Irritable Bowel Syndrome (IBS) for PLAB 1

Irritable Bowel Syndrome (IBS) is a common, chronic functional gastrointestinal disorder characterized by abdominal pain, bloating, and changes in bowel habits. Understanding its diagnosis, management, and red flags is crucial for PLAB 1 preparation.

Definition and Pathophysiology

Diagnostic Criteria

The diagnosis of IBS is primarily clinical, based on symptoms and the exclusion of other organic diseases. The Rome IV criteria are the most widely used diagnostic guidelines.

Rome IV Criteria for IBS	Key Features
Recurrent abdominal pain	On average, at least 1 day per week in the last 3 months
Associated with defecation	Pain is related to passing stool
Associated with change in stool frequency	More frequent or less frequent stools
Associated with change in stool form	Harder, lumpier, or looser, watery stools
Duration	Symptoms must have started at least 6 months before diagnosis

Subtypes of IBS

IBS is further classified based on the predominant stool pattern:

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IBS with Constipation (IBS-C)

Characterized by hard or lumpy stools at least 25% of the time and loose or watery stools less than 25% of the time.

IBS with Diarrhea (IBS-D)

Characterized by loose or watery stools at least 25% of the time and hard or lumpy stools less than 25% of the time.

IBS with Mixed Bowel Habits (IBS-M)

Characterized by loose or watery stools at least 25% of the time and hard or lumpy stools at least 25% of the time.

IBS Unsubtyped (IBS-U)

Individuals who do not meet the criteria for IBS-C, IBS-D, or IBS-M.

Red Flags: When to Suspect Organic Disease

It is crucial to differentiate IBS from more serious conditions. The presence of 'red flag' symptoms warrants further investigation to rule out organic pathology such as inflammatory bowel disease (IBD), malignancy, or celiac disease.

Red Flags for IBS:

Unexplained weight loss
Rectal bleeding or blood in stool
Nocturnal symptoms (pain or diarrhea waking the patient from sleep)
Anemia
Onset of symptoms after age 50
Family history of IBD or colorectal cancer
Persistent vomiting
Abdominal mass

Management of IBS

Management is individualized and focuses on symptom relief and improving quality of life. It typically involves a combination of lifestyle modifications, dietary changes, and pharmacological interventions.

Lifestyle and Dietary Modifications

Dietary Fiber: Gradual increase in soluble fiber (e.g., psyllium) can help regulate bowel movements. Insoluble fiber may worsen symptoms for some.
FODMAP Diet: A low-FODMAP diet (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols) can be effective for many patients, but should be undertaken with guidance from a dietitian.
Regular Meals: Eating regular meals and avoiding skipping meals.
Fluid Intake: Adequate hydration.
Stress Management: Techniques like mindfulness, yoga, or cognitive behavioral therapy (CBT).

Pharmacological Management

Medications are used to target specific symptoms:

For Constipation (IBS-C): Laxatives (e.g., macrogol), secretagogues (e.g., linaclotide, plecanatide).
For Diarrhea (IBS-D): Antidiarrheals (e.g., loperamide), bile acid sequestrants, 5-HT3 receptor antagonists (e.g., alosetron - restricted use).
For Abdominal Pain: Antispasmodics (e.g., hyoscine butylbromide, mebeverine), low-dose tricyclic antidepressants (TCAs) or selective serotonin reuptake inhibitors (SSRIs) for visceral hypersensitivity.
For Bloating: Simethicone, probiotics (evidence is mixed).

Key Takeaways for PLAB 1

What are the core diagnostic criteria for IBS according to Rome IV?

Recurrent abdominal pain on average at least 1 day/week in the last 3 months, associated with defecation, change in stool frequency, or change in stool form, with symptom onset at least 6 months prior.

List three 'red flag' symptoms that would prompt further investigation beyond IBS diagnosis.

Unexplained weight loss, rectal bleeding, nocturnal symptoms (any one of these).

What is a common dietary intervention for IBS that involves restricting certain types of carbohydrates?

The low-FODMAP diet.

The gut-brain axis is a bidirectional communication system between the central nervous system (brain) and the enteric nervous system (gut). In IBS, this axis is thought to be dysregulated, leading to altered gut motility, increased visceral sensitivity, and changes in mood and behavior. This can manifest as pain, bloating, and altered bowel habits. Understanding this connection is key to managing IBS, as stress and psychological factors can significantly impact symptoms, and conversely, gut symptoms can affect mood.

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Learning Resources

Irritable Bowel Syndrome - NHS(documentation)

Provides a comprehensive overview of IBS, including symptoms, causes, diagnosis, and management from the UK's National Health Service.

Rome Foundation - Rome IV Criteria(documentation)

The official source for the Rome IV diagnostic criteria for functional gastrointestinal disorders, including IBS.

Irritable Bowel Syndrome (IBS) - Patient Education(blog)

A patient-focused explanation of IBS, covering symptoms, causes, diagnosis, and treatment options.

Low FODMAP Diet for IBS - Monash University(documentation)

Information from the leading researchers on the low-FODMAP diet, including its role in IBS management.

Irritable Bowel Syndrome (IBS) - BMJ Best Practice(documentation)

A clinical decision support tool for healthcare professionals, offering in-depth guidance on IBS diagnosis and management.

Irritable Bowel Syndrome (IBS) - Mayo Clinic(documentation)

A detailed overview of IBS from a reputable medical institution, covering symptoms, causes, risk factors, and treatment.

Gastroenterology - Irritable Bowel Syndrome (IBS) - MSD Manual Professional Version(documentation)

A comprehensive medical reference for healthcare professionals on IBS, including pathophysiology, diagnosis, and treatment.

Understanding the Gut-Brain Axis - Harvard Health(blog)

Explains the complex relationship between the gut and the brain, which is central to understanding IBS.

Irritable Bowel Syndrome (IBS) - Medscape(documentation)

A detailed medical overview of IBS, including epidemiology, etiology, clinical manifestations, diagnosis, and management strategies.

IBS: What You Need to Know - American College of Gastroenterology(documentation)

Patient-friendly information from a leading gastroenterology organization, covering symptoms, diagnosis, and management of IBS.