30th July 2023

Intestinal causes

Coeliac disease

Coeliac disease is an autoimmune condition in which autoantibodies are produced in response to the protein gliadin found in wheat. It is pathologically characterised by chronic inflammation, crypt hyperplasia and villous atrophy of the small bowel, especially the duodenum. The immune response is mediated by T cells, and hence is a type IV hypersensitivity reaction.

It has 2 peaks of presentation – childhood, when gluten is first introduced into the diet, and early middle age, which is the commonest age of onset in the UK.

The typical presentation is of chronic abdominal pain, postprandial bloating, diarrhoea (often steatorrhea due to the malabsorption), weight loss, fatigue, and in children, failure to thrive. It is often associated with anaemia. Extraintestinal manifestations include dermatitis herpetiformis and arthralgia.

Suspected coeliac disease can be screened for by testing tissue transglutaminase antibodies (anti-tTGA) and IgA anti-endomysial antibodies (anti-EMA IgA). Total IgA levels should also be checked, as IgA deficiency can lead to false negatives. The gold standard diagnostic test is endoscopy, with at least 5 biopsy samples required from different (duodenal) sites. It is essential that a patient continues to eat gluten for the 6 weeks preceding this, or false negatives can occur. The mainstay of treatment is complete elimination of gluten from the diet.

Complications include micronutrient deficiencies, and it is also associated with osteoporosis, hyposplenism, and an increased risk of GI lymphoma.

Inflammatory bowel disease (IBD)

Crohn’s disease and ulcerative colitis can both lead to malabsorption, but this is more common in Crohn’s disease. Malabsorption occurs due to the chronic inflammation of the bowel impairing the ability of the GI tract to absorb nutrients. Malabsorption may also be a consequence of bowel resections, which are sometimes required to treat refractory IBD.

More information on the diagnosis, clinical features and management of IBD can be found in the Bowel Infection and Inflammation topic.

Tropical sprue

Tropical sprue is a condition which can be seen in travellers to tropical regions, and presents with acute or chronic diarrhoea, leading to malabsorption. Folic acid and vitamin B12 are particularly common associated deficiencies. The exact aetiology is unknown, but it is thought to have an infectious cause. It causes pathological features similar to coeliac disease, as bowel mucosa over time will exhibit crypt hyperplasia and villous atrophy.

There is no targeted treatment, and management is instead supportive, including fluid and electrolyte correction, treatment of anaemia, and replacement of any deficient micronutrients.

Whipple’s disease

Caused by infection with Tropheryma whipplei, and has a preponderance to middle aged men. Initially presents with abdominal pain, diarrhoea/steatorrhoea, and weight loss, and is associated with arthralgia, lymphadenopathy and hyperpigmentation of the skin. If untreated, it can progress to affect the CNS and heart, with the most serious consequences including seizures, ataxia, endocarditis and myocarditis.

Diagnosis involves upper GI endoscopy, and a key feature is villous granules that are strongly positive for the Periodic acid-Schiff stain.

Treatment involves 2 weeks of IV ceftriaxone or benzylpenicillin, followed by a 1-year maintenance treatment of oral co-trimoxazole. In cases where the CNS or heart is involved, oral doxycycline and hydroxychloroquine are also given.

Chronic diarrhoeal illnesses

Any chronic diarrhoeal illness can lead to malabsorption, as any intake will not be able to be appropriately absorbed, and over time they can cause chronic inflammation in the gut, which impairs absorption.

As well as other primary bowel diseases already discussed, infectious illnesses such as giardiasis can cause chronic diarrhoea. Giardiasis by the protozoan Giardia lamblia, and is frequently seen in travellers and people living in areas with poor sanitation. Generally self-limiting, it can be treated with metronidazole, if required.

Short gut syndrome

This refers to, quite literally, the occurrence of a shorter than normal small bowel, generally due to bowel resection in the treatment of various diseases, or due to congenital abnormalities. Having a reduced amount of bowel impairs the ability of the GI tract to absorb nutrients. Management is supportive, with nutritional supplements generally required, and even parenteral nutrition in severe cases.