Malabsorption

Malabsorption is a state arising from abnormality in digestion or absorption of food nutrients across the gastrointestinal(GI) tract.

Impairment can be of single or multiple nutrients depending on the abnormality. This may lead to malnutrition and variety of anaemias^[1].

Some prefer to classify malabsorption clinically into three basic categories^[2]:

(1) selective, as seen in lactose malabsorption;

(2) partial, as observed in a-Beta-lipoproteinemia, and

(3) total as in celiac disease.

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Pathophysiology

The main purpose of the GI tract is to digest and absorb nutrients (fat, carbohydrate, and protein), micronutrients (vitamins and trace minerals), water, and electrolytes. Digestion involves both mechanical and enzymatic breakdown of food. Mechanical processes include chewing, gastric churning, and the to-and-fro mixing in the small intestine. Enzymatic hydrolysis is initiated by intraluminal processes requiring gastric, pancreatic, and biliary secretions. The final products of digestion are absorbed through the intestinal epithelial cells.

Malabsorption constitutes the pathological interference with the normal physiological sequence of digestion (intraluminal process), absorption (mucosal process) and transport (postmucosal events) of nutrients^[3].

Intestinal malabsorption can be due to:^[4]

• Mucosal damage (enteropathy)
• Congenital or acquired reduction in absorptive surface
• Defects of specific hydrolysis
• Defects of ion transport
• Pancreatic insuffeciency
• Impaired enterohepatic circulation

Causes

Clinical features

  It can present in variety of ways and features might give clue to underlying condition. Symptoms can be intestinal or extra-intestinal, former predominates in severe malabsorption.

• Diarrhoea, often steatorrhoea is the most common feature. Watery, diurnal and nocturnal, bulky, frequent stools are the clinical hallmark of overt malabsorption. It is due to impaired water, carbohydrate and electrolyte absorption or irritation from unabsorbed fatty acid. Latter also result in bloating, flatulence and abdominal discomfort. Cramping pain usually suggest obstructive intestinal segment e.g. in Crohn's disease especially if persists after defecation.^[3]
• Weight loss can be significant despite increased oral intake of nutrients^[6].
• Growth retardation, failure to thrive, delayed puberty in children
• Swelling or oedema from loss of protein
• Anaemias, commonly from vitamin B12, folic acid and iron deficiency presenting as fatigue and weakness.
• Muscle cramp from decreased vitamin D, calcium absorption. Also lead to osteomalacia and osteoporosis
• Bleeding tendencies from vitamin K and other coagulation factor deficiencies.
• Low serum tryptophan and clinical depression, as can happen with fructose malabsorption

Diagnosis

There is no specific test for Malabsorption. As for most medical conditions, investigation is guided by symptoms and signs. Moreover, tests for pancreatic function are complex and varies widely between centres.

Blood Tests

• Routine blood tests may reveal anaemia, high ESR or low albumin; which has high sensitivity for presence of organic disease ^[7][8]. In this setting, microcytic anaemia usually implies iron deficiency and macrocytosis can be from impaired folic acid or B12 absorption or both. Low cholesterol or triglyceride may give clue toward fat malabsorption as low calcium and phosphate toward osteomalacia from low vitamin D.
• Specific vitamins like vitamin D or micro nutrient like zinc levels can be checked. Fat soluble vitamins (A, D, E & K) are affected in fat malabsorption. Prolonged prothrombin time can be from vitamin K deficiency.
• Serological studies

Specific tests are carried out to determine underlying cause.

IgA tissue trans glutamate or IgA antiendomysium assay for gluten sensitive enteropathy.

Stool studies

• Microscopy is particularly useful in diarrhoea, may show protozoa like giardia, ova, cyst and other infective agents.
• Fecal fat study to diagnose steatorrhoea is less frequently performed nowadays.
• Low elastase is indicative of pancreatic insufficiency. Chymotrypsin and pancreolauryl can be assessed as well^[9]

Radiological studies

• Barium follow through is useful in delineating small intestinal anatomy. Barium enema may be undertaken to see colonic or ileal lesions.
• CT abdomen is useful in ruling out structural abnormality, done in pancreatic protocol when visualising pancreas.
• Magnetic resonance cholangiopancreatography (MRCP) to complement or as an alternative to ERCP

Interventional studies  

• Endoscopy is frequently undertaken, but to visualise small intestine which can be up to 7m long is indeed a daunting task.

OGD to reveal duodenal lesion also for D2 biopsy (for celiac disease, tropical sprue, Whipple disease, A-b-lipoproteinemia etc.)

Enteroscopy for enteropathy and jejunal aspirate and culture for bacterial overgrowth

Colonoscopy is helpful in colonic or ileal lesion.

• ERCP

Other investigations

• Radio isotope tests e.g. 75SeHCAT, 95mTc to exclude terminal ileal disease.
• Sugar probes or sub 51Cr-EDTA to determine intestinal permeability^[3].
• Glucose hydrogen breath test for bacterial overgrowth
• D-xylose absorption test. lower level in urine after ingestion indicates bacterial overgrowth or reduced absorptive surface. normal in pancreatic insufficiency.
• Bile salt breath test to determine bile salt malabsorption.
• Schilling test to establish cause of B12 deficiency.
• Lactose H2 breath test for lactose intolerance

Management

Treatment is directed largely towards management of underlying cause.

• Replacement of nutrients, electrolytes and fluid may be necessary. In severe defeciency hospital admission may be required for parentral administration, often advice from dietician is sought. People whose absortive surface are severely limited from disease or surgery may need long term total parenteral nutrition. Pancreatic enzymes are supplemented orally in insuffeciencies.
• Dietary modification is important in some conditions. Life long avoidance of particular food or food constituent may be needed in Celiac disease or lactose intolerence.
• Bacterial overgrowth usually respond well to course of antibiotic. Use of cholestyramine to bind bile acid will help reducing diarrhoea in bile acid malabsorption.

See also

• Fructose malabsorption
• Protein losing enteropathy

References