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 diagnostic 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: highest prevalence in individuals aged 20–39 ^[1]

References:^[1][2][3][4]

Epidemiological data refers to the US, unless otherwise specified.

IBS is a functional gastrointestinal disorder without a specific organic cause. The pathophysiological processes leading to IBS are multifaceted and not yet fully understood. The most common findings associated with IBS are:

• Altered gastrointestinal motility
• Visceral hypersensitivity/hyperalgesia
• Altered permeability of the gastrointestinal mucosa
• Psychosocial aspects

References:^[3][5][6][7]

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 related to 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!

References:^[2][3]

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

• IBS-D (diarrhea is the predominant symptom)
• IBS-C (constipation is the predominant symptom)
• IBS‑M (mixed diarrhea and constipation)
• IBS‑A (alternating diarrhea and constipation)

References:^[3]

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.

References:^[2][3][8]

Other differential diagnoses to consider

• Bacterial or viral gastroenteritis
• Hypothyroidism/hyperthyroidism
• Celiac disease
• Lactose intolerance
• Bacterial overgrowth syndrome (i.e., SIBO)

References:^[3]

The differential diagnoses listed here are not exhaustive.

General measures

• Regular consultations and reassurance that the disease, although chronic, is benign
• Lifestyle changes
  • 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:

• Diarrhea
  • Antidiarrheals (loperamide)
  • Rifaximin
  • Alosetron ^[9]
  Constipation
  • Soluble fibers/bulk‑forming laxatives (psyllium)
  • Osmotic laxatives (polyethylene glycol)
  • Lubiprostone (chloride channel activator)
• Cramping/pain
  • Antispasmodics (dicyclomine, hyoscyamine)
  • Tricyclic antidepressants (e.g., amitriptyline, nortriptyline)