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Gastrointestinal (GI) System

Irritable bowel syndrome (IBS)

Complex, functional gastrointestinal disorder characterized by chronic abdominal pain or discomfort and altered bowel habits.

Complex, functional gastrointestinal disorder characterized by chronic abdominal pain or discomfort and altered bowel habits.


Epidemiology

  • ♀ > ♂ (3x)
IBS prevalence in population studies around the world
IBS prevalence in population studies around the world | Enck, P., Aziz, Q., Barbara, G., Farmer, A. D., Fukudo, S., Mayer, E. A., … Spiller, R. C. (2016). Irritable bowel syndrome. Nature Reviews Disease Primers, 2(1), 16014. https://doi.org/10.1038/nrdp.2016.14

Classification

  • Constipation-predominant IBS (IBS-C) or BSFS type 1/2)
  • Diarrhoea predominant IBS (IBS-D) or BSFS type 6/7

  • Mixed subtype IBS (IBS-M) (M/C)
  • Postinfectious IBS (IBS-PI): Characterized by persistent abdominal pain and diarrhoea, typically following an episode of infectious gastroenteritis.
Irritable bowel syndrome subtypes
Irritable bowel syndrome subtypes. | IBS: irritable bowel syndrome; IBS-C: IBS with constipation; IBS-D: IBS with diarrhoea; IBS-M: IBS with constipation/diarrhoea; IBS-U: IBS unclassifiable. | Lacy et al., 2016

Etiology

Disease associations:

IBS-associated comorbidities
IBS-associated comorbidities: A model of irritable bowel syndrome (IBS) and its associations with other clinical, intestinal, extra-intestinal and psychiatric conditions. The different components should be viewed as layers of complexity: the IBS subtypes are part of the group of functional bowel disorders, these are part of all kinds of functional disorders and these again are part of a `layer’ of psychiatric disorders. | GERD, gastroesophageal reflux disease; IBS-C, IBS with constipation; IBS-D, IBS with diarrhoea; IBS-M, mixed-type IBS; IBS-U, unsubtyped IBS; PMS, premenstrual syndrome. | Enck, P., Aziz, Q., Barbara, G., Farmer, A. D., Fukudo, S., Mayer, E. A., … Spiller, R. C. (2016). Irritable bowel syndrome. Nature Reviews Disease Primers, 2(1), 16014. https://doi.org/10.1038/nrdp.2016.14

Postinfectious IBS (IBS-PI):

Conceptual model for post-infectious IBS
Conceptual model for post-infectious IBS | Thabane, M., & Marshall, J. K. (2009). Post-infectious irritable bowel syndrome. World journal of gastroenterology, 15(29), 3591–3596. https://doi.org/10.3748/wjg.15.3591

Pathophysiology

Gut-brain-axis:

Serotonin (5-HT) may contribute to the postprandial symptoms of these patients and provide a rationale for the use of serotonin antagonist in the treatment of this disorder.
  • Cortical structures associated with IBS:
    • Mid cingulate cortex
    • Prefrontal lobe 
Graphical summary of pathways involved in IBS
Graphical summary of pathways involved in IBS | Ng, Q. X., Soh, A., Loke, W., Lim, D. Y., & Yeo, W. S. (2018). The role of inflammation in irritable bowel syndrome (IBS). Journal of inflammation research, 11, 345–349. https://doi.org/10.2147/JIR.S174982

Visceral hypersensitivity:

  • Increased end-organ sensitivity with recruitment of “silent” nociceptors
  • Spinal hyperexcitability with activation of nitric oxide and possibly other neurotransmitters
  • Endogenous (cortical and brainstem) modulation of caudal nociceptive transmission
  • Development of neuroplasticity

IBS-D:

  • High-amplitude propagating contractions (HAPCs)
  • Rapid colonic transit and accompanied by abdominal pain

Presentation

Defining features of IBS are the presence of recurrent abdominal pain in association with altered bowel habits (diarrhoea, constipation or both). The spectrum, duration and severity of symptoms can range from inconvenient to incapacitating and can prevent individuals from participating in everyday activities.

Favour diagnosis:

  • Abdominal pain or discomfort which improves with defecation
  • Association of symptoms with stress or emotional upset
  • Absence of fever and weight loss
  • Small volume stools
  • No evidence of blood in stools

Against diagnosis:

  • First time in old age
  • Progressive course
  • Persistent diarrhoea after a 48 hour fast
  • Presence of nocturnal diarrhoea
  • Steatorrheal stools
Patient features supportive of an IBS diagnosis
Patient features supportive of an IBS diagnosis or raising concern for organic pathology. | IBS: irritable bowel syndrome; IBD: inflammatory bowel disease; GI: gastrointestinal. | Moayyedi, P., Mearin, F., Azpiroz, F., Andresen, V., Barbara, G., Corsetti, M., … Tack, J. (2017). Irritable bowel syndrome diagnosis and management: A simplified algorithm for clinical practice. United European Gastroenterology Journal, 5(6), 773–788. https://doi.org/10.1177/2050640617731968

Diagnosis

Rome IV diagnostic criteria:

Recurrent abdominal pain, on average, at least 1 day/week in the last 3 months associated with ≥ 2 of the following for the last 3 months with symptom onset at least 6 months before diagnosis.
  1. Related to defecation
  2. Associated with a change in the stool frequency
  3. Associated with a change in the stool form (appearance)
Irritable bowel syndrome (IBS) diagnosis
Simplified algorithm for irritable bowel syndrome (IBS) diagnosis. | Moayyedi, P., Mearin, F., Azpiroz, F., Andresen, V., Barbara, G., Corsetti, M., … Tack, J. (2017). Irritable bowel syndrome diagnosis and management: A simplified algorithm for clinical practice. United European Gastroenterology Journal, 5(6), 773–788. https://doi.org/10.1177/2050640617731968

Management

Management algorithm for irritable bowel syndrome
Management algorithm for irritable bowel syndrome. | FODMAP: fermentable oligosaccharides, disaccharides, monosaccharides and polyols; SSRIs: selective serotonin re-uptake inhibitors; TCAs: tricyclic antidepressants. | Moayyedi, P., Mearin, F., Azpiroz, F., Andresen, V., Barbara, G., Corsetti, M., … Tack, J. (2017). Irritable bowel syndrome diagnosis and management: A simplified algorithm for clinical practice. United European Gastroenterology Journal, 5(6), 773–788. https://doi.org/10.1177/2050640617731968

Dietary management:

  • Low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet: Ingestion of FODMAPs such as lactose, fructose, or sorbitol, alone or in combination, produce gut symptoms such as gas and diarrhoea.
  • Low lipids

5HT3 antagonists:

  • Alosetron | S/E: Ischaemic colitis
  • Tegaserod | S/E: Cardiac toxicity.
  • Lubiprostone| S/E: Nausea, headache, diarrhea, allergic reactions, and dyspnea.

Antidepressants:

  • SSRI:
    • Paroxetine in IBS – C
    • Citalopram for pain and IBS – D
  • TCA:
    • Imipramine in IBS – D
    • Desipramine in IBS – D and abdominal pain

Summary:

IBS
Enck, P., Aziz, Q., Barbara, G., Farmer, A. D., Fukudo, S., Mayer, E. A., … Spiller, R. C. (2016). Irritable bowel syndrome. Nature Reviews Disease Primers, 2(1), 16014. https://doi.org/10.1038/nrdp.2016.14

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