Irritable Bowel Syndrome


Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal (GI) disorder characterized by abdominal pain and altered bowel habits in the absence of a specific and unique organic pathology, although microscopic inflammation has been documented in some patients.Population-based studies estimate the prevalence of irritable bowel syndrome at 10-20% and the incidence of irritable bowel syndrome at 1-2% per year.

Signs and symptoms

Manifestations of IBS are as follows:

  • Altered bowel habits
  • Abdominal pain
  • Abdominal bloating/distention

 Altered bowel habits in IBS may have the following characteristics:

  • Constipation variably results in complaints of hard stools of narrow caliber, painful or infrequent defecation, and intractability to laxatives
  • Diarrhea usually is described as small volumes of loose stool, with evacuation preceded by urgency or frequent defecation
  • Postprandial urgency is common, as is alternation between constipation and diarrhea
  • Characteristically, one feature generally predominates in a single patient, but significant variability exists among patients

Abdominal pain in IBS is protean, but may have the following characteristics:

  • Pain frequently is diffuse without radiation
  • Common sites of pain include the lower abdomen, specifically the left lower quadrant
  • Acute episodes of sharp pain are often superimposed on a more constant dull ache
  • Meals may precipitate pain
  • Defecation commonly improves pain but may not fully relieve it
  • Pain from presumed gas pockets in the splenic flexure may masquerade as anterior chest pain or left upper quadrant abdominal pain
  • Additional symptoms consistent with irritable bowel syndrome are as follows:
    • Clear or white mucorrhea of a noninflammatory etiology
    • Dyspepsia, heartburn
    • Nausea, vomiting
    • Sexual dysfunction (including dyspareunia and poor libido)
    • Urinary frequency and urgency have been noted
    • Worsening of symptoms in the perimenstrual period
    • Comorbid fibromyalgia
    • Stressor-related symptoms
    Symptoms not consistent with irritable bowel syndrome should alert the clinician to the possibility of an organic pathology. Inconsistent symptoms include the following:
    • Onset in middle age or older
    • Acute symptoms (irritable bowel syndrome is defined by chronicity)
    • Progressive symptoms
    • Nocturnal symptoms
    • Anorexia or weight loss
    • Fever
    • Rectal bleeding
    • Painless diarrhea
    • Steatorrhea
  • Gluten intolerance Diagnosis The Rome IV criteria for the diagnosis of irritable bowel syndrome require that patients have had 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:
    • Related to defecation (may be increased or unchanged by defecation)
    • Associated with a change in stool frequency
    • Associated with a change in stool form or appearance
      The Rome IV criteria (May 2016) only require abdominal pain in defining this condition; “discomfort” is no longer a requirement owing to its nonspecificity, and the recurrent abdominal pain.  Supporting symptoms include the following:
    • Altered stool frequency
    • Altered stool form
    • Altered stool passage (straining and/or urgency)
    • Mucorrhea
    • Abdominal bloating or subjective distention
      Four bowel patterns may be seen with irritable bowel syndrome, and these remain in the Rome IV classification.These patterns include the following:
    • IBS-D (diarrhea predominant)
    • IBS-C (constipation predominant)
    • IBS-M (mixed diarrhea and constipation)
    • IBS-U (unclassified; the symptoms cannot be categorized into one of the above three subtypes)
      The usefulness of these subtypes is debatable. Notably, within 1 year, 75% of patients change subtypes, and 29% switch between constipation-predominant IBS and diarrhea-predominant IBS. The Rome IV criteria differ from the Rome III criteria in basing bowel habits on stool forms solely during days with abnormal bowel movements rather than on the total number of bowel movements.   A comprehensive history, physical examination, and tailored laboratory and radiographic studies can establish a diagnosis of irritable bowel syndrome in most patients. The American College of Gastroenterologists does not recommend laboratory testing or diagnostic imaging in patients younger than 50 years with typical IBS symptoms and without the following “alarm features” :
    • Weight loss
    • Iron deficiency anemia
    • Family history of certain organic GI illnesses (eg, inflammatory bowel disease, celiac sprue, colorectal cancer)
      Screening studies to rule out disorders other than IBS include the following:
    • Complete blood count with differential to screen for anemia, inflammation, and infection
    • A comprehensive metabolic panel to evaluate for metabolic disorders and to rule out dehydration/electrolyte abnormalities in patients with diarrhea
    • Stool examinations for ova and parasites, enteric pathogens, leukocytes,Clostridium difficile toxin, and possibly Giardia antigen
      History-specific studies include the following:
    • Hydrogen breath testing to exclude bacterial overgrowth in patients with diarrhea and to screen for lactose and/or fructose intolerance
    • Tissue transglutaminase antibody testing and small bowel biopsy in IBS-D to diagnose celiac disease.
    • Thyroid function tests
    • Serum calcium testing to screen for hyperparathyroidism
  • Erythrocyte sedimentation rate and C-reactive protein measurement are nonspecific screening tests for inflammation Management Management of irritable bowel syndrome consists primarily of providing psychological support and recommending dietary measures. Pharmacologic treatment is adjunctive and should be directed at symptoms.  Dietary measures may include the following:
    • Fiber supplementation may improve the symptoms of constipation and diarrhea
    • Polycarbophil compounds (eg, Citrucel, FiberCon) may produce less flatulence than psyllium compounds (eg, Metamucil)
    • Judicious water intake is recommended in patients who predominantly experience constipation
    • Caffeine avoidance may limit anxiety and symptom exacerbation
    • Legume avoidance may decrease abdominal bloating
    • Lactose, fructose, and/or FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) should be limited or avoided in patients with these contributing disorders
    • Probiotics are being studied for their use in decreasing IBS symptoms
      Although the evidence is mixed regarding long-term improvement in GI symptoms with successful treatment of psychiatric comorbidities, the American College of Gastroenterology has concluded the following:
    • Psychological interventions, cognitive-behavioral therapy, dynamic psychotherapy, and hypnotherapy are more effective than placebo
    • Relaxation therapy is no more effective than usual care
      Pharmacologic agents used for the management of symptoms in IBS include the following:
    • Anticholinergics (eg, dicyclomine, hyoscyamine)
    • Antidiarrheals (eg, diphenoxylate, loperamide)
    • Tricyclic antidepressants (eg, imipramine, amitriptyline)
    • Prokinetics
    • Bulk-forming laxatives
    • Serotonin receptor antagonists (eg, alosetron)
    • Chloride channel activators (eg, lubiprostone)
    • Guanylate cyclase C (GC-C) agonists (eg, linaclotide)
    • Antispasmodics (eg, peppermint oil, pinaverium, trimebutine, cimetropium/dicyclomine)
    • Potentially, rifaxamin (this is still investigational and not FDA approved)

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