Failing to identify the less common causes of chronic diarrhoea
There are some infections to consider in patients with persisting diarrhoea. Some of these have an acute onset, with clinical features of an acute GI infection, but some may lack an apparent acute phase. Giardia duodenalis (formerly G. lamblia or G. intestinalis) is endemic worldwide. It is a relatively common cause of travellers' diarrhoea, particularly among backpackers and campers, but should also be considered in immunocompromised patients and in men who have sex with men (MSM).17 Even if symptoms usually resolve after 2-4 weeks, the infection may persist longer (chronic giardiasis) or becomes the starting point for post-infection IBS.18 The diagnosis of chronic giardiasis relies on identifying the Giardia cysts or trophozoites in stool samples. Importantly, in the absence of travel in high-risk areas, routine stool testing for ova and parasites is unlikely to identify important causes of chronic diarrhoea.19
Whipple's disease caused by Tropheryma whipplei is uncommon, with an estimated prevalence of 1-6/106, even if asymptomatic carriage of the bacteria is much more common (1-10% in different geographical areas). However, this diagnosis should be considered for unexplained long-standing diarrhoea.20 It is characterized by gastrointestinal manifestations secondary to malabsorption due to the affected small bowel mucosa, i.e., chronic diarrhoea, abdominal pain, and accompanying weight loss. In addition, arthralgia and arthritis mimicking rheumatoid arthritis most often precede the diarrhoea by years. The diagnosis is primarily obtained from multiple specimens' duodenal biopsies with histopathology (PAS staining, immunohistochemistry). Furthermore, depending on the symptom profile, PCR-based tests of mucosal tissue or other biologic material are highly recommended.
A somewhat debated bacterial aetiology explaining chronic diarrhoea is small intestinal bacterial overgrowth (SIBO),21 mainly due to imprecise and not agreed-upon definitions with clinical relevance. The original description defines it as a malabsorption syndrome in predisposed individuals due to anatomic, pharmacologic, or other changes that promote stasis of intestinal contents and impaired resistance to bacteria. On the other hand, if SIBO is defined more widely by a pathologic glucose or lactulose hydrogen breath test, data supports the role of SIBO also in diarrhoea-dominated functional bowel disorders. However, its relative importance is still debatable. Widespread use of antibiotic treatment based on a combination of symptoms compatible with a functional bowel disorder and a positive hydrogen breath test does not have a worldwide consensus. This most probably mirrors a variation in microbiota composition and function, different from the original SIBO concept (figure 1).
|Abnormal small intestinal motility
|Diabetic visceral neuropathy
Idiopathic intestinal pseudo-obstruction
Amyloidosis Muscular dystrophy
Chronic use of opioids or other motility suppressing drugs
|Small intestinal stricture
Post-surgical alteration in anatomy (e.g. blind loop, ileocecal resection)
|Inherited immune deficiencies (e.g. common variable immune deficiency)
Acquired immune deficiency (AIDS, severe malnutrition
|Long-term acid suppression
Irritable bowel syndrome
End-stage liver or renal disease
Figure 1. Examples of diseases associated with small intestinal bacterial overgrowth
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