58. Functional bowel diseases

Page created on April 11, 2022. Not updated since.

Introduction and epidemiology

Functional bowel disorders (FBDs) are disorders characterised by gastrointestinal symptoms in the absence of organic disease of the gastrointestinal tract.

Like other functional disorders, FBDs are associated with many other conditions, including other functional disorders, fibromyalgia, chronic fatigue syndrome, GERD, non-cardiac chest pain, and psychiatric disorders like depression, anxiety, and somatisation.

Functional bowel disorders are common, but significantly underdiagnosed. The prevalence is 10%, and they’re more common in young women. These disorders do not progress to severe organic disease but can severely affect life quality.


The pathomechanism of functional bowel disorders is not well known, but some patients have motor abnormalities of the GI tract. Selective hypersensitisation of visceral afferent nerves in the GI tract, mucosal immune system activation, and psychosocial factors may be involved. In many cases, the disorder begins after a GI infection.

One theory regarding the pathomechanism of IBS is that carbohydrates which are difficult to digest, so-called fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs), contribute to the symptoms.


There are many types, but these are the most common:

  • Irritable bowel syndrome (IBS) – chronic abdominal pain and altered bowel habits
    • Diarrhoea-predominant irritable bowel syndrome – IBS-D
    • Constipation-predominant irritable bowel syndrome – IBS-C
  • Functional dyspepsia
  • Functional constipation
  • Functional diarrhoea
  • Functional chest pain
  • Functional heartburn
  • Globus sensation – sensation of a lump or tightness in the throat

As is typical for functional disorders, the symptoms usually vary in intensity and have periodic exacerbations. Functional heartburn is a common cause of failure of PPI treatment for heartburn.

Diagnosis and evaluation

Diagnosis of functional bowel disorders requires ruling out organic causes of the symptoms, often involving endoscopy with biopsy, testing for faecal calprotectin and parasites, and coeliac disease. Diagnosis is based on the Rome IV criteria, which requires the criteria for that functional bowel disorder to be fulfilled for the last 3 months, with symptoms onset at least 6 months prior to diagnosis.


As with other functional disorders, it’s important to communicate the diagnosis to the patient correctly to avoid the patient feeling like they’re not being taken seriously.

Unfortunately, there’s no causative therapy, only symptomatic:

  • Diarrhoea – loperamide
  • Constipation – psyllium husk, polyethylene glycol
  • Abdominal pain – smooth muscle relaxants, TCAs

Psychotherapy and avoidance of FODMAP may also be helpful.

Treatment of functional chest pain primarily focuses on neuromodulation of pain with the use of antidepressants and behavioural therapy.

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