Gastrointestinal Malabsorption

Malabsorption is a failure to fully absorb nutrients from the gastrointestinal tract. There are many causes including abnormalities of the gut wall, failure to produce digestive enzymes and abnormalities of gut flora.

The outcome is malnutrition. Malnutrition may also be caused by inadequate diet with or without malabsorption.

Malabsorption, from whatever cause, may be accompanied by:

• Changes in weight and growth:
  • Inadequate absorption of calories will lead to loss of weight in adults or stunting of growth in children.
  • Adults will complain of unintentional weight loss and perhaps tiredness, lethargy and fatigue.
  • Children may have similar symptoms accompanied by failure to thrive with growth failure (falling through the centile charts for height and weight).
• Gastrointestinal symptoms:
  • Chronic diarrhoea is common. Chronic diarrhoea may be defined as the abnormal passage of three or more loose or liquid stools per day for more than four weeks and/or a daily stool weight greater
    than 200 g/day.
  • Steatorrhoea is often present. There is excessive fat in the stools and they become pale, bulky and offensive in smell. Stools float and are difficult to flush away. They often leave a greasy rim around the pan.
• Signs of deficiencies may be apparent:
  • There may be non-anaemic iron deficiency.
  • Iron deficiency anaemia
  • Folate deficiency or vitamin B12 deficiency.
  • Bleeding may result from low vitamin K.
  • Oedema occurs in protein/ calorie malnutrition.

There may also be clinical features associated with the particular cause of malabsorption. The commonest causes in the UK are coeliac disease, Crohn's disease and chronic pancreatitis.

Mucosal causes

• Coeliac disease usually presents in childhood but can present later. It is due to allergy to gluten in the diet that results in subtotal villous atrophy. This considerably reduces the surface area available for absorption. A diet strictly free of gluten will reverse the process. Nowadays, about 1 child in 4 with coeliac disease is diagnosed by targeted screening rather than presenting with malabsorption.¹
• Cows' milk intolerance.²
• Soya milk intolerance.
• Infection:
  • Immune deficiency. In HIV infection, malnutrition is nearly as important as opportunistic infection, especially in countries with access to HAART.³
  • Giardiasis.
  • Whipple's disease.
  • Intestinal tuberculosis.
  • Tropical sprue.
  • Traveller's diarrhoea.
  • Diphyllobothriasis (tapeworm can cause B12 malabsorption).
  • Ancylostomiasis (Hook worm).
  • Strongyloidiasis (nematode).
• In patients with an inflammatory bowel disorder and malabsorption, an immune deficiency should be considered.⁴
• Intestinal lymphectasia and other causes of lymphatic obstruction include lymphoma, tuberculosis and cardiac disease.

Intraluminal causes

• Pancreatic insufficiency:
  • Cystic fibrosis usually presents in children who have respiratory problems, although the malabsorption may be the presenting feature. Sweat test will be positive.
  • Chronic pancreatitis can cause both inadequacy of enzyme production and bicarbonate secretion.⁵ It often follows attacks of acute pancreatitis and years of alcohol abuse. Plain abdominal x-ray may show calcification of the pancreas.
  • Carcinoma of pancreas.
  • Zollinger-Ellison syndrome.
• Defective secretions of bile salts due to cholestatic jaundice or disease of the terminal ileum.
• Drugs.

Structural causes

• Intestinal hurry:
  • Post gastrectomy
  • Post vagotomy
  • Gastrojejunostomy
• The blind loop syndrome involves disturbance normal of gut flora with malabsorption. This can occur after surgery for peptic ulcer such as Billroth II or Polya gastrectomy. These operations have rarely been required since about 1980 with the modern management of peptic ulcer disease but the effects may not be manifest for many years. Abnormalities of bowel flora causing malabsorption can occur in immune deficiencies.⁴
• Fistulae.
• Diverticulae and strictures.
• Crohn's disease.
• Amyloidosis.
• Short bowel syndrome.⁶
• Eosinophilic gastroenteropathy.
• Mesenteric arterial insufficiency.
• Radiation enteritis.

Causes outside the gut

• Hyperthyroidism
• Hypothyroidism
• Addisons' disease
• Diabetes mellitus
• Hyperparathyroidism
• Hypoparathyroidism
• Carcinoid syndrome
• Widespread skin disease (rapid cell turnover may also affect gut mucosa)
• Malnutrition
• Collagen diseases
• Eating disorders
• Factitious diarrhoea due to purgative abuse

In the elderly, causes of malabsorption are as in the young but pancreatic insufficiency can occur without obvious cause and intestinal overgrowth can occur without anatomical abnormality of the bowel.⁷

The British Society of Gastroenterology have produced guidelines for the investigation of chronic diarrhoea.⁸

Blood tests

• FBC
• Plasma viscosity
• Vitamin B12 level
• Red cell folate
• Iron status (usually ferritin but can be iron and iron binding capacity)
• Clotting screen for vitamin K deficiency
• Serum albumin
• Calcium (corrected for albumin level)
• Anti-endomyseal, anti-reticulin and alpha-gliadin antibodies (coeliac screen)
• Liver function tests
• Serum magnesium

Iron deficiency causes a microcytic blood picture. Folate or vitamin B12 deficiency causes megaloblastic anaemia but the picture may be mixed.

In those thought to have IBS, the incidence of undiagnosed coeliac disease is high but it is important not to over-investigate this group.⁸

Patients with unexplained iron deficiency merit screening for coeliac disease.⁹

Stool

• Faecal microbiological assessments may be indicated.
• Sudan stain for fat globules.

Imaging and endoscopy

• Barium follow through may show structural abnormalities.
• Endoscopy and small bowel biopsy is very useful.
• ERCP may be needed (biliary tree assessment).
• Enteroscopy may have an increasing role.

Breath hydrogen tests

Take samples of end-expired air; give glucose; take more samples at half-hour intervals. If there is bacterial overgrowth there is an increase in exhaled hydrogen 1h after ingestion. This test is better than tests using radioactive 14C bile salts.

Management depends upon the cause. For example:

• Coeliac disease requires a strict gluten free diet.
• Pancreatic insufficiency requires the oral administration of enzymes with food.
• Blockage of the flow of bile requires surgery.
• Crohn's disease usually responds to steroids.
• Blind loop syndromes may require further surgery.
• Where bile salts are not reabsorbed, it may be necessary to give resins to bind them.¹⁰
• If there is folate deficiency and possibly B12 deficiency too, it is imperative to give an injection of vitamin B12 before starting folate supplementation. Otherwise there is a risk of precipitating subacute combined degeneration of the cord.

Complications are related to the underlying disease.

• Lassitude is common. Children will have stunted growth.
• Untreated coeliac disease may result in small bowel adenocarcinoma or lymphoma.
• Infertility is common, especially in coeliac disease.
• Anaemia may occur.
• Rickets, osteoporosis or osteomalacia may occur.

Before it was superseded by endoscopy, small bowel biopsy was performed with the Crosby capsule: This is swallowed on the end of a tube, and is monitored by x-ray screening until it reaches the jejunum. It is fired by suction, and a biopsy is caught in its jaws. It is then pulled back up.