Sechenov School
Home › Pathophysiology › Irritable Bowel Syndrome

Irritable Bowel Syndrome

Syndromum intestini irritabilis

For medical students2 min readUpdated 2026-10-10

Irritable Bowel Syndrome (IBS) is a common functional gastrointestinal disorder characterized by a chronic and recurrent complex of digestive symptoms. Patients regularly experience abdominal pain or significant discomfort, along with changes in bowel habit frequency and stool consistency.

EpidemiologyThe condition affects a significant portion of the global population, estimated at 15% to 20%.
LocalizationThe pathological process predominantly involves the large intestine (colon).
DurationTo confirm the syndrome, symptoms must persist for at least 12 weeks over the course of a year.
CriteriaRequires the presence of at least two persistent signs of intestinal dysfunction.

Clinical Presentation and Diagnostic Criteria

The pathophysiological essence of the syndrome lies in the development of a persistent symptom complex affecting the lower gastrointestinal tract. As noted, the process primarily localizes to the colon, where basic physiological processes of fecal formation and excretion are disrupted.

To establish a diagnosis of IBS, a clear temporal criterion must be met: functional disorders must persist for at least 12 weeks within a single calendar year.

Additionally, abdominal pain or discomfort must be accompanied by at least two persistent signs of intestinal dysfunction from the following list:

Role of Neurohumoral Regulation and Psychosomatics

Mechanisms of central nervous system regulation and local balance of biologically active substances play a monumental role in the pathogenesis of irritable bowel syndrome.

First, a specific patient personality type is identified as a major risk factor. IBS patients are frequently characterized by:

  1. Hysterical and aggressive behavioral reactions.
  2. Depressive episodes and obsessive states.
  3. Hypochondriacal manifestations and cancerophobia (pathological fear of developing a malignant tumor).

Second, a local imbalance of biologically active substances occurs. The disruption of adequate bowel regulation is directly linked to altered concentrations and activity of a cascade of mediators and hormones, involving:

Dietary Risk Factors

In addition to psychological and neurohumoral aspects, a crucial trigger for IBS development is the dietary factor (the patient's nutritional habits).

Two primary dietary habits contribute to the pathology:

Expected consequences of such eating behavior include profound functional shifts. The motor-evacuation function of the digestive tract alters. Following motility disturbances, the normal ratio of intestinal microflora shifts (dysbiosis develops), closing the vicious cycle of IBS pathogenesis and exacerbating flatulence, pain, and stool disorders.

Mnemonic

Remember the "2–12" rule for IBS diagnosis: you need at least 2 persistent symptoms of bowel dysfunction that trouble the patient for a total of at least 12 weeks in a year.

Frequently asked questions

What clinical subtypes of IBS are distinguished based on predominant stool consistency according to the Bristol Stool Scale?

Based on predominant stool consistency, four main clinical subtypes of irritable bowel syndrome are distinguished:

  • IBS with constipation (IBS-C) — predominant constipation.
  • IBS with diarrhea (IBS-D) — predominant diarrhea.
  • Mixed IBS (IBS-M) — characterized by alternating constipation and diarrhea.
  • Unclassified IBS — non-specific disease course variant.
What organic gastrointestinal diseases require differential diagnosis with IBS?

Differential diagnosis of irritable bowel syndrome must be performed with several organic diseases that can mimic this condition:

  • Inflammatory bowel disease (IBD)
  • Celiac disease
  • Lactose and fructose intolerance
  • Microscopic colitis
  • Colonic neoplasms
What is the pathophysiological mechanism of visceral hypersensitivity in irritable bowel syndrome?

The basis of IBS pathogenesis is impaired neuroendocrine regulation along the brain-gut axis. The key mechanism is the development of visceral hypersensitivity, leading to intestinal motor dysfunction.

Triggers for visceral hypersensitivity can include prior enteric infections, local inflammatory processes, intestinal trauma, and food allergies.

IBS patients also show increased GI barrier permeability; normalization of the mucosal-epithelial barrier permeability is stated as a therapeutic goal for agents like rebamipide.

Which pharmacological drug classes are used for the targeted therapy of various IBS subtypes?

For IBS pharmacotherapy, the following groups and agents are indicated:

  • Antispasmodics — baseline therapy regardless of IBS subtype; various groups are used for pain, including trimebutine, mebeverine, hyoscine butylbromide, pinaverium bromide.
  • Trimebutine — a synthetic regulator; used in IBS patients to reduce pain and normalize stool frequency and consistency. Its effects include normalizing bowel motility and raising the pain threshold.
  • For IBS with predominant diarrhea: loperamide, diosmectite, rifaximin, probiotics, alongside antidiarrheal drugs and enterosorbents.
  • For IBS with predominant constipation: laxatives, including psyllium preparations, macrogol, lactulose, and/or prucalopride.
  • For microbiota correction: prebiotics and probiotics.
  • Amitriptyline — prescribed for adults to reduce abdominal pain when antispasmodics are ineffective; contraindicated in children under 18.
How many signs of intestinal dysfunction are required for diagnosis?

The syndrome must be accompanied by at least two persistent signs (e.g., passage of mucus, flatulence, altered stool frequency or consistency).

Which part of the gastrointestinal tract is primarily affected in IBS?

The pathological process in irritable bowel syndrome is primarily localized in the colon.

Which biologically active substances (BAS) are involved in regulatory dysfunction in IBS?

The imbalance involves serotonin, histamine, bradykinin, cholecystokinin, neurotensin, VIP (vasoactive intestinal peptide), as well as enkephalins and endorphins.

How do refined foods affect the development of the pathology?

The predominance of refined foods in the diet and irregular meals alter motor-evacuation function and disrupt the balance of intestinal microflora.

Go deeper

More topics in Pathophysiology

EnteropathyPubertal DisordersLeukocytosis and LeukopeniaChronic ColitisOvarian Pathology and HypogonadismChanges in the Leukocyte DifferentialPrinciples of Endocrinopathy TherapyPathology of the Hemostatic System: Thrombocytopenias and ThrombocytopathiesUlcerative Colitis: Pathophysiology and Clinical PresentationThrombotic SyndromeArterial HyperemiaPrinciples of Therapy for Digestive DisordersPathophysiology →