• Clinical science

Irritable bowel syndrome


Irritable bowel syndrome (IBS) is a common chronic condition affecting 20–50% of patients with gastrointestinal complaints. The exact pathophysiology is unknown, but may involve changes in gastrointestinal motility, visceral hypersensitivity, and altered gastrointestinal permeability. The condition presents with recurrent, non‑specific changes in bowel movements (e.g., diarrhea and/or constipation) and abdominal symptoms (e.g., diffuse pain, pressure). The Rome IV diagnositc criteria, which are based on alterations in bowel habits, are used to diagnose IBS. Laboratory studies and imaging reveal no abnormalities. Treatment consists of dietary modifications and administration of symptom‑based medication (antidiarrheals, laxatives, antispasmodics).


  • Prevalence: 10–20% in North America and Europe (accounts for 20–50% of referrals to gastroenterologists)
  • Sex: : In Western countries, women are 1.5–2 times more likely to be affected than men.
  • Age: Approx. 50% of cases are reported in individuals younger than 35.


Epidemiological data refers to the US, unless otherwise specified.


IBS is defined as a functional gastrointestinal disorder without a specific organic cause. The underlying pathophysiology of IBS is not yet fully understood. The following pathophysiological hypotheses describe the most common findings associated with IBS, though these may not be present in every case.

  • Altered gastrointestinal motility
    • Increased meal transit time, often resulting in diarrhea, or reduced meal transit time, often resulting in constipation.
    • Generalized hyperresponsiveness of smooth muscles may be observed
  • Visceral hypersensitivity/hyperalgesia
    • Increased perception of physiological intestinal movements
    • Pain caused by hypersensitivity to
      • Balloon distention of the intestine (sudden, rather than gradual, distention)
      • Abdominal bloating
  • Altered permeability of the gastrointestinal mucosa
    • Possibly mild intestinal inflammation
    • Postinfectious
      • Infections with bacteria, viruses, protozoans, and helminths
      • Further risk factors → young age, prolonged infection with fever
    • Altered intestinal microflora
    • Food sensitivity
  • Psychosocial aspects
    • Increased occurrence of IBS in patients with depression, anxiety, phobias, somatization
    • Conversely, patients with IBS report higher levels of stress


Clinical features

IBS is characterized by chronic abdominal pain and changes in bowel habits – both of which are typical, but not specific, symptoms of the condition.

  • Abdominal pain
    • Frequency, intensity, and localization generally vary widely from patient to patient
    • Typically alleviated by defecation
  • Altered bowel habits: diarrhea and/or constipation
  • Other gastrointestinal symptoms
    • Nausea, reflux, early satiety
    • Passing of mucus, abdominal bloating
  • Extraintestinal symptoms
    • Generalized somatic symptoms (e.g., pain or fatigue, as in fibromyalgia)
    • Disturbed sexual function
    • Dysmenorrhea
    • Increased urinary frequency and urgency
  • Physical examination: normal

Red flag symptoms: nighttime diarrhea and abdominal pain, fever, bloody stools, weight loss and acute onset of symptoms!

Subtypes and variants

Four different patterns are seen in the presentation of irritable bowel syndrome:



IBS is a clinical diagnosis; based on the patient's history (Rome IV criteria) and symptoms. However, any suspected differential diagnoses should be ruled out before making a definitive diagnosis.

Patient history

  • Rome IV criteria for irritable bowel syndrome: diagnosis can be made if the following criteria are present
    • Recurrent abdominal pain on average at least 1 day per week during the previous 3 months that is associated with 2 or more of the following:
      • Pain related to defecation
      • Change in stool frequency
      • Change in stool form or appearance
  • Other symptoms consistent with IBS (see "Symptoms/clinical findings")
  • A family history of inflammatory bowel disease, celiac disease, or colorectal cancer is unusual in patients with IBS.

Ruling out organic disease

If no other differential diagnosis is suspected, laboratory tests and imaging are generally not recommended for individuals under the age of 50 if they show typical signs of IBS and lack any alarming signs, such as iron-deficiency anemia, weight loss, or a family history of organic gastrointestinal diseases.

  • Laboratory tests: normal in IBS
  • Stool analysis: normal in IBS
    • No blood or leukocytes
    • Negative cultures and parasites
  • Hydrogen breath test: to rule out lactose or fructose tolerance test http://goo.gl/7Mb2ah
  • Imaging:
    • Normal colonic mucosa on colonoscopy
    • Other imaging includes abdominal ultrasound, barium studies, CT


Differential diagnoses

General appearance Pain Stool habits
Irritable bowel syndrome
  • Healthy; no weight loss
  • Alleviated by defecation; diffuse; no nighttime pain
Crohn's disease
  • Weight loss; malnourishment
  • Usually constant; occurs particularly in the right lower abdomen; may appear at night
  • Non‑bloody, watery diarrhea; increased frequency; possible nighttime diarrhea
Ulcerative colitis
  • Weight loss only in severe cases
  • Mostly left lower abdomen; may occur at night
Colorectal carcinoma
  • Weight loss

Other differential diagnoses to consider


The differential diagnoses listed here are not exhaustive.


General measures

  • Regular consultations and reassurance that the disease, although chronic, is benign
  • Dietary adjustments
    • Plenty of fluid
    • High‑fiber foods
    • Avoidance of:
      • Gas‑producing foods (e.g., beans, onions, prunes)
      • Fermentable, short‑chain carbohydrates (e.g., foods with high fructose content: honey, apples, corn syrup)
      • Lactose
      • Gluten
  • Physical activity
  • Stress management (identification of stress factors, avoidance techniques, relaxation therapy)
  • Psychological therapy (patients with psychological conditions): e.g., cognitive-behavioral therapy

Medical therapy

Medical therapy of IBS is symptom‑directed: