Irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic condition that is very common in North America and Europe. It is thought that the underlying pathophysiology involves changes in gastrointestinal motility, visceral hypersensitivity, and altered gastrointestinal permeability. Patients present with recurrent abdominal pain associated with changes in stool frequency, form, and/or appearance. IBS is a clinical diagnosis based on the Rome IV criteria for IBS and ruling out alternative diagnoses. Nonpharmacological treatment includes dietary modifications (e.g., avoidance of trigger foods) and psychobehavioral therapies. Pharmacological therapies such as loperamide, laxatives, and lubiprostone are targeted to diarrhea, constipation, and global IBS symptoms, respectively.

• 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]
• Associated conditions ^[2]
  • Somatic pain syndromes: fibromyalgia, chronic fatigue syndrome, functional chest pain
  • Psychiatric disorders: major depressive disorder, anxiety disorder, somatization disorder
  • Gastrointestinal disorders: GERD, functional dyspepsia

References:^[1][3]

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:^[4][5]

IBS is characterized by chronic abdominal pain and changes in bowel habits (see also “Rome IV criteria for IBS”).

• 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

Several subtypes of IBS exist and are defined by stool quality. ^[6]

• IBS-D: diarrhea is the predominant symptom
• IBS-C: constipation is the predominant symptom
• IBS‑M: mixed diarrhea and constipation
• IBS-U: criteria for IBS are met but bowel movements can't be categorized into the above subgroups

IBS is a clinical diagnosis (using the Rome IV criteria for IBS). Limited diagnostic studies are recommended for the primary purpose of ruling out alternative diagnoses.

Approach ^[6]

• Evaluate for diagnostic criteria for IBS.
• Screen for red flag symptoms (see “Differential diagnoses”).
• Obtain a limited diagnostic workup to rule out alternative diagnoses.

An acute change in bowel habits, signs of overt GI bleeding, or other red flags for CRC should prompt further diagnostic evaluation.

Rome IV criteria for irritable bowel syndrome ^[7]

All of the following criteria must be met to diagnose IBS.

• Timing: ≥ 6 months since the onset of symptoms
• Symptoms
  • Recurrent abdominal pain (≥ 1 day per week during the previous 3 months)
  • PLUS ≥ 2 of the following
    • Abdominal pain related to defecation
    • Change in stool frequency
    • Change in appearance of stool

Laboratory studies ^[6][8]

The following studies should routinely be considered to rule out alternative etiologies :

• All patients: CBC (anemia requires further evaluation)
• In patients with diarrhea
  • Fecal calprotectin and CRP
  • Celiac disease serology
  • Stool testing for giardiasis ^[9]
• In patients with relevant symptoms and history
  • Thyroid function tests
  • Diagnostics for infectious gastroenteritis

Colonoscopy ^[8]

• Only recommended in patients:
  • With red flags for CRC
  • Due for age-appropriate screening for CRC ^[8]

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

Other differential diagnoses to consider

• Bacterial or viral gastroenteritis
• Hypothyroidism/hyperthyroidism
• Celiac disease
• Lactose intolerance
• Bacterial overgrowth syndrome (i.e., SIBO)
• See also: “Differential diagnoses of acute abdominal pain”
• See also: “Causes of chronic diarrhea”
• See also: “Causes of constipation”

The differential diagnoses listed here are not exhaustive.

Currently, there are no curative treatments for IBS. Management is focused on treating the associated symptoms.

Nonpharmacological treatment ^[8]

• Dietary adjustments
  • Soluble fiber supplements (e.g., psyllium) ^[8]
  • Avoidance of trigger foods (e.g., trial of elimination diet)
    • Low FODMAP diet: diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols
    • Consider the support of a registered dietitian.
• Lifestyle changes ^[6]
  • Regular physical activity
  • Stress management (e.g., relaxation techniques)
• Psychobehavioral therapy ^[6]
  • Patient-centered care, strong therapeutic alliance
  • Gut-directed psychotherapy (i.e., cognitive behavioral therapy and hypnotherapy)
• Adjunctive therapy: peppermint oil for global symptom relief ^[8][10]

Elimination diets that restrict fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (i.e., a low FODMAP diet) should be undertaken with the support of a registered dietitian in order to avoid nutritional deficiencies. ^[8]

Pharmacotherapy ^[8]

• Evidence for pharmacological therapy is mixed and recommendations vary between guidelines.
• Consult a specialist for refractory symptoms and/or long-term treatment.

Diarrhea ^[11]

• Loperamide
• Rifaximin
• Alternative medications: include alosetron (a selective 5-HT3 receptor antagonist), eluxadoline (opioid agonist/antagonist)

When treating IBS-associated diarrhea, use caution to avoid constipation as an adverse effect, especially in patients with IBS-M or IBS-U.

Constipation ^[12]

• Polyethylene glycol (PEG) ^[11][12]
• Alternative medications:
  • Intestinal secretagogues
  • Tenapanor
    • A sodium-hydrogen antiporter 3 inhibitor
    • Increases water secretion into the intestinal lumen and has antinociceptive effects.
  • Tegaserod: a partial 5-HT₄ receptor agonist

Abdominal pain ^[8][11][12]

The following can be considered to treat associated abdominal pain:

• Antispasmodics: e.g., dicyclomine, hyoscyamine
• Tricyclic antidepressants: e.g., amitriptyline (off-label) ^[8]

Disposition ^[13]

• IBS may be managed in an outpatient setting; arrange for close follow-up.
• Provide patients with return precautions if alarm features develop (see “Clinical features”).