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Abstract
Disordered intestinal absorption is not a single condition but rather it involves many conditions that have many causes and therefore various clinical presentations. Therefore, there is no uniform management, instead a management strategy tailored for individual cases. This essay aims to review, yet comprehensively, malabsorption syndrome about types, pathophysiology, diagnosis, consequences, and treatment.
Introduction
Disordered intestinal absorption is not a single condition but rather it involves many conditions that have many causes and therefore various clinical presentations. Defective absorption affects large sized molecules (macromolecules) as proteins, fats and carbohydrates, or small sized ones (micro molecules) as minerals and vitamins, or both. The underlying defect is disturbance in intra-luminal absorption, terminal absorption (at the brush border of the small intestine), or defective transport across the intestinal epithelium (Scott, 1975). Any of the previous conditions is associated with defective absorption of one nutrient or more and is termed malabsorption syndrome. As the term signals a patho-physiological condition rather than provide an aetiological perception; therefore, malabsorption is not an ideal definitive clinical diagnosis (Binder, 2005).
Diarrhoea is the most prevalent symptom, which may be fatty diarrhoea (steatorrhoea) with excretion of 6% or more of the daily fat dietary intake. Secondary systemic disorders may occur as pernicious anaemia, which may result because of absent intrinsic factor needed for vitamin B12 absorption (Binder, 2005). Depending on the underlying disturbance, bone diseases (osteomalacia or osteoporosis) and or hypoproteinaemia may result (Scott, 1975).
Definition, and classification of malabsorption syndrome
Definition of malabsorption syndrome
Greenson (2005) defined malabsorption syndrome as any type or degree of small intestine dysfunction affecting the physical absorption of a substance normally absorbed from or retained in the small intestine. Montalto and others (2008) defined malabsorption syndrome as a disorder of mal-digestion and or malabsorption extending beyond the compensating mechanisms of the small intestines that result in manifestations of nutrients deficiency.
Classification of malabsorption syndrome
In 1960, Adlersberg suggested classifying malabsorption syndrome into a primary and a secondary types. The primary type includes coeliac disease and tropical sprue. The primary type is genetically transmitted or environmentally determined. Alternatively, environmental factors interact with genetic predisposition to excite or lessen the disorders manifestations. Adlersberg (1960) inferred that such a distinction between the primary and secondary type is important as diseases producing the secondary type (infective as Whipples disease, or anatomical as short bowel syndrome) should be investigated and treated whenever possible.
Shaffer, Thomson, and others (2000), agreed with Scott (1975) that a classification based on the possible causes of malabsorption would be helpful in management and raise clinical suspicion indices as to the diagnosis and management. They classified malabsorption syndrome in two broad categories, disorders of digestion, and disorders of absorption. Digestion disorders may result from defective mixing action of the stomach as in cases of partial gastrectomy.
Further, they may result because of pancreatic insufficiency (secondary to cystic fibrosis, inflammation or tumours), or because of bile salt deficiency as with liver diseases, biliary disease or ileal resection. Defective absorption may result from loss of absorptive surface whether surgical, mucosal damage, inflammation (as in Crohns disease) or infections and infestations. Isolated biochemical abnormalities as disaccharidase deficiency can produce a type of malabsorption syndrome determined by the underlying deficiency.
Montalto and others (2008) recognized the difficulty in having a uniformly agreed upon classification of malabsorption syndromes is because of the complicated nature of the absorption process, which occurs and is influenced by many organs, and the effect of many diseases on the absorption mechanisms.
Causes of malabsorption syndrome
Causes of malabsorption syndromes are many. Table (1) [see appendix 1] summarizes the different aetiologies of malabsorption syndromes based on the classification suggested by Shaffer, Thomson et al (2000).
Diseases of the small intestine
Scott (1975), Shaffer, Thomson, and others (2000) pointed the main small intestinal disorders that cause malabsorption is short bowel syndrome, stagnant (blind) loop syndrome, tropical sprue. Bacterial infection (Whipples disease), parasitic infestations, and small bowel infiltration by amyloidosis, or lymphoma are other causes pointed by the authors.
Parrish (2005) provided a coherent and systematic review on short bowel syndrome focusing on how to capitalize on the remaining bowel part. The syndromes definition is defective small intestine absorptive capacity because of decreased length or decreased functional length of the bowel. The causes differ in frequency between adults and children; in adults, surgical resection as a treatment for obesity or tumour resection, and vascular accidents (embolism and or thrombosis of the mesenteric vessels) are the commonest causes. In children, the commonest causes are necrotizing enterocolitis, narrowing of the intestinal lumen by volvulus, hernia, and intussusceptions. Other causes in both age groups include Crohns disease, radiation enteritis, trauma, and abdominal tumours (Parrish, 2005).
Diarrhoea and steatorrhoea are cardinal symptoms, in addition, manifestations caused by increased gastric secretions and intestinal motility changes are usually present. In addition, osmotic drag of water and electrolytes to the small bowel lumen worsens diarrhoea. Changes in GIT motility in the form of increased transit rate, and decreased gastric emptying rate result in a degree of stagnation of intestinal contents, which is a risk factor to increased growth of small intestinal (Parrish, 2005).
Tropical sprue is characterised by persistent and prolonged diarrhoea, it is endemic in many Asian countries, some Caribbean islands, and parts of South America; therefore called travellers diarrhoea. This suggests environmental factors present in endemic areas; American soldiers serving in Vietnam suffered the disease, which calls for high suspicion index for military and other Servicemen cases appearing in Afghanistan and other endemic areas (Khokhar, 2004).
In his retrospective descriptive study on chronic diarrhoea patients is conducted in Islamabad (Pakistan) between 1994 and 2003. Khokhar (2004) inferred the disease aetiology is still unknown but a pleomorphic virus similar to orthomyxovirus and corona virus was identified in some adult and children cases. All patients in the series reviewed showed megaloblastic anaemia because of B12 and Folic acid deficiency. Treatment is mainly by tetracycline, folic acid supplementation, and fluid and electrolyte replacement during the acute phase (Khokhar, 2004).
Whipples disease (intestinal lipodystrophy) is a rare disease affecting mainly middle-aged men, caused by Tropheryma whippelii, and the main characteristic is chronic diarrhoea and arthritis. The organism may be present in the environment evidenced by morphological relationship to actinomycetes; and isolation of the organisms DNA in the gastric juice of 10 % and the saliva of 30% of healthy individuals. Currently, there is not enough data available on specific antibodies against the organism isolated from patient. Treatment is by tetracyclines for long periods up to two years (Dutly and Altwegg, 2001).
Coeliac disease
Coeliac disease is a chronic inflammatory disorder affecting the small intestine (the jejunum more than the ileum) and has genetic predisposition (Scott, 1975). Torres and colleagues (2007) reviewed the recent concepts in coeliac disease focusing on pathogenesis, prevalence, and diagnosis and inferred the chronic inflammatory process is T-cell mediated which results in the autoimmune characteristics of the disease.
The main disease characteristic is the bodys immune response to ingested wheat gluten and related proteins of rye and barley. This response is the cause of the chronic inflammatory process that results in atrophy of intestinal villi, and hyperplasia of the intestinal crypts. The disease affects children and adults and is the commonest small bowel disease caused by food allergy in humans, the disease prevalence in North America and Europe ranges from one in 100 to one in 300.
Green and Cellier (2007) stated the disease develops only if the individual has one of two or more alternative forms (alleles) of HLA (Human Leukocyte Antigen) gene. These alleles occupy the same position locus on paired chromosomes and control the same inherited characteristic (HLA-DQ2, and HLA-DQ8).
Epidemiological studies suggest that environmental factors play an important role in developing coeliac disease traits. These factors are the protective effect of breast-feeding, and the timing of introducing gluten contained food to weaning (at four month age carries a high risk, while at seven months carries a marginal risk). Second, Rotavirus gastrointestinal infections increase the risk to develop coeliac disease traits early in life (Green and Cellier, 2007).
Gluten ingestion triggers coeliac disease traits; the alcohol-soluble gliadin is the main component of gluten protein that forms the main toxic bulk. The undigested molecules of gliadin make amino acids fractions resistant to enzymatic degradation by gastric, pancreatic, and small intestinal brush borders protease enzymes. Thus, these chains remain in the small bowels lumen to cross the epithelial barrier on increased intestinal permeability as when infection by Rotavirus occur to interact with antigen-presenting cells in the lamina propria resulting in immune reaction and consequently the chronic inflammatory process (Green and Cellier, 2007).
The clinical picture of coeliac disease vary with age, in infants and young children the presenting symptom is usually diarrhoea, abdominal distension, vomiting, anorexia, and failure to thrive are common complaints at this age group. In older children and adolescents, extra-intestinal manifestations are more common as short stature, and anaemia. In adults, females are more commonly affected than males (2-3 to 1) with dominating symptoms of iron deficiency anaemia and osteoporosis (Green and Cellier, 2007).
Torres and colleagues (2007) pointed to the changing pattern of clinical presentation of the disease in adults as diarrhoea, and abdominal discomfort becoming more common. Besides, iron deficiency anaemia and osteoporosis manifestations are becoming common presentations in silent cases without diarrhoea.
Diagnosis of coeliac disease needs duodenal biopsy that displays intra-epithelial lymphocytosis, villous atrophy, and crypt hyperplasia. Indications for serological tests are persistent unexplained abdominal discomfort with or without malabsorption symptoms or irritable bowel syndrome. The most sensitive antibody tests for diagnosis are the immunoglobulin A (IgA) class (Green and Cellier, 2007).
Pancreatic diseases causing malabsorption
Exocrine pancreatic insufficiency may result from chronic pancreatitis, pancreatic tumours, resection, or genetically determined cystic fibrosis (Scott, 1975). Cystic fibrosis is caused by a recessive gene on autosomal chromosome 7, estimated to be present in 4% of individuals. This gene controls movements of water and electrolytes across the cell wall; therefore, faulty gene results in increased electrolytes and decreased water entering the cell, subsequently secretions become thicker to obstruct secretory glands ducts.
Turnpenny and Ellard (2007) stated that 85% of cystic fibrosis patients have pancreatic ducts blocked by the thick secretions resulting in obstruction of pancreatic enzymes release with subsequent malabsorption and steatorrhoea. Besides steatorrhoea, diabetes may or may not be present, with occasional abdominal pain, and duodenal biopsy may be normal. Picture of complications like pseudo cyst formation and or biliary obstruction may be present. Lundh test (low trypsin on feeding a standard meal) is positive. Treatment includes pancreatic extract, and low fat and high protein diet (Diakowska and others, 2006).
Pathophysiology
There are three phases of absorption in the small intestine. First is the luminal phase during which hydrolysis and breaking down of carbohydrates, proteins, and fat ingested occur, this phase depends on pancreatic and biliary enzymes. Second is the mucosal phase, during which final hydrolysis of dietary food elements occur, and absorbing the hydrolysed molecules by intestinal mucosal cells processing them in preparation for cellular transfer and export. Third is the transport phase where the absorbed nutrients are transferred to blood and lymph circulation. Both second and third phases depend mainly on the functional and anatomical integrity of the intestinal mucosa (Sedlack and Viggiano, 2008).
About minerals and vitamins, Sedlack and Viggiano (2008) stated that absorption of iron, calcium, magnesium, and water-soluble vitamins occurs in the duodenum and jejunum. Fat-soluble vitamins (A, K, D, E, and B12) absorption occurs in the ileum, taking in consideration the jejunum cannot adapt to absorb fat-soluble vitamins whereas the ileum can adapt to absorb minerals and vitamins.
Dietary carbohydrates are mainly in the form of starch, disaccharides, and glucose and can only be absorbed in the small intestine as monosaccharides. This mandates primary digestion by pancreatic amylase enzyme and disaccharidases enzymes secreted by the small intestine brush border. Lactose (milk disaccharide) needs digestion by lactase enzyme secreted by the small intestine brush border. Dietary proteins are in the form of polypeptides and need massive hydrolysis to smaller sized units (dipeptides or tripeptides) a process called proteolysis. This process is aided by pepsin enzyme secreted from the stomach (chief cells) as pepsinogen.
Proteolysis also needs trypsinogen and other peptidases enzyme secreted from the exocrine pancreas (acinar cells). Enterokinase enzyme secreted by the small intestine brush border activates these pro-enzymes to pepsin, and trypsin. Thus, enterokinase deficiency results in hypoproteinaemia. Dietary fat is commonly available in food as triglycerides acted upon by pancreatic lipase to produce fatty acids and glycerol. Transformation of these simpler products to chylomicrons occurs by the intestinal mucosal cells before being absorbed into the circulation through lymphatic circulation (Binder, 2005).
There are three different mechanisms for diarrhoea in malabsorption syndrome, Sedlack and Viggiano (2008) explained these mechanisms as follows. Osmotic diarrhoea where water-soluble molecules are not absorbed and retained in the small intestinal lumen; thus, increasing the inside osmotic pressure. This results in stool volume less than a litre per day with increased osmolar gap but diarrhoea stops on fasting.
Lactase deficiency, sorbitol rich foods (a sugar used in diabetic sweet diet) and excessive use of antacids cause this type of diarrhoea. In secretory diarrhoea, there is abnormal water and electrolyte transport through the intestine, in other words, the intestine secretes rather than absorbs. In this case, the stool volume is more than a litre per day, and is more like extracellular fluid in osmolarity and composition.
Diarrhoea does not stop on fasting, and the condition occurs on exposure to bacterial toxins, steatorrhoea, over use of laxatives, and hormone-secreting tumours as Zollinger-Ellison syndrome. The problem in exudative diarrhoea (third mechanism) is abnormal permeability of intestinal mucous membrane to allow transfer of serum proteins, mucous or blood into the intestine lumen. It occurs in invasive bacterial infections (as shigellosis), inflammatory, ulcerative or infiltrative bowel disease. Motility GIT disorders may take a rapid transit form as in short bowel syndrome where diarrhoea is because of malabsorption, or take a delayed (slow) transit form, where diarrhoea is because of bacterial overgrowth as in stagnant loop syndrome (Sedlack and Viggiano, 2008).
Diagnosis
A road map to diagnosis of malabsorption syndrome is shown in appendix two figures two (initial assessment) and three (further assessment) (Schiller, 2004).
Based on the request of the Chairman of the British Societys clinical services committee, Thomas and colleagues (2003) published the second edition of guidelines to investigate a case of chronic diarrhoea. Based on these guidelines, initial evaluation includes history of present illness, diarrhoea of more than three months, accompanied by weight loss, mainly continuous or nocturnal, and large volume of stools are suggestive of organic disease. Positive family history may raise suspicion on coeliac disease or inflammatory bowel disease. Medical history may suggest short bowel syndrome, pancreatic disease, a systemic disease, or a drug induced diarrhoea.
Thorough examination is useful in diagnosis and assessment, dry tongue and skin point to dehydration, oedema point to hypoproteinaemia. Associated iron deficiency anaemia suggests proximal small intestine malabsorption, examining the stools for blood or occult blood is a wise practice in these cases. Associate metabolic bone disease, osteoporosis or osteomalacia, points to defects in calcium and protein absorption that is proximal bowel malabsorption. Hyper-pigmentation points to the possibility of Whipple disease, coeliac disease, or eosinophilic gastroenteritis. Associated arthritis commonly points to Whipples disease or ulcerative colitis.
Initial investigations include complete blood picture, ESR, C-reactive protein, liver function tests, blood urea, serum electrolytes, folate, serum iron, and Schilling test for vitamin B12 malabsorption. Although these tests have a high specificity; yet, they have low sensitivity as an indication for organic disease. Although infectious diarrhoea is uncommon in immuno-competent patient, yet stool culture and microscopic examination should be done.
Qualitative faecal fat stain and quantitative faecal fat determination are needed to diagnose steatorrhoea. Specific stool tests as faecal elastase (for pancreatic enzymes), stool osmolality and measuring the osmotic gap help to distinguish the diarrhoea mechanism. Stool analysis for fat, blood, and markers of inflammation (as lactoferrin) are helpful tests to assess the cause of diarrhoea. Serological tests as antiendomysium antibodies help to diagnose coeliac disease (Thomas and colleagues, 2003).
Further evaluation includes mainly distal duodenal biopsy may show Howell-Jolly bodies in cases of coeliac disease (interpreted with other findings as there are many causes for differential diagnosis). Small bowel imaging (barium follow through) reserved to cases where distal duodenal biopsy is negative. Non-invasive techniques as Technetium hexa-methyl-propylene amine labelled leukocyte scanning is helpful to diagnose inflammatory disease especially Crohns disease (Thomas and colleagues, 2003).
Nutritional consequences of malabsorption syndrome
Malabsorption is a serious condition to all age groups; however, it is of special importance in young age groups as infants and children are growing, the associated nutritional deficiencies may cause enduring growth and development (both physical and mental) disabilities. Dehydration that warrants fluid therapy is common in all age groups; however, cases of hypoproteinaemia with oedema may be an exception.
Electrolyte and vitamin deficiencies need special care for diagnosis and replacement treatment. Remote consequences of malabsorption may affect all body systems, chronic inflammation of the GIT mucosa because of the disease, or associated vitamin deficiency aggravates the condition. Anaemia specially iron deficiency and megaloblastic are common occurrences. Abnormal bleeding tendency because of vitamin K deficiency may also occur.
Osteoporosis and osteomalacia are also common because of calcium, magnesium, vitamin D, and protein malabsorption, calcium deficiency gives rise to tetany. Amenorrhoea, impotence, and infertility may occur because of nutritional deficiencies. Hyperparathyroidism resulting from calcium and vitamin D deficiency may also occur. Nervous system disorder may occur with peripheral neuritis secondary to vitamin deficiency is the commonest. Skin affection occurs in the form of hyperkeratosis secondary to vitamin A, zinc, essential fatty acid deficiencies, petechiae and purpuric rash secondary to vitamin K deficiency occurs (Semrad and Powell, 2008).
Prognosis and treatment
In mild cases, the main treatment objective is to maintain hydration and nutrition through symptom control using antidiarrheal agents as bismuth subsalicylate. In moderate to severe cases or cases associated with other clinical manifestations as fever, anaemia, blood or fat in the stools, or dehydration or changes in serum electrolytes, treatment strategy focuses on replacement therapy, and specific cause therapy (Scott, 1975).
Non-specific treatment is targeted to dietary modification, where it is advisable to have smaller and more frequent meals. Limit gas producing food, straw use, and chewing gums. Limiting spices, and fibres in meals, lactose, gluten rich foods (in coeliac disease), and fats in steatorrhoea are advisable measures. However, vitamin and mineral supplements are advisable early (Jeejeebhoy, 2002). Intravenous nutrition indications are dehydration, electrolytes disturbances, emergency conditions (as bleeding, toxaemia, or postoperative). Oral nutrition is the preferred route to maximize the calorie content from fats and carbohydrates, and maximize the protein content, taking in consideration not to worsen the diarrhoea (Sedlack, and Viggiano, 2008).
Every effort should be made to reach an aetiological diagnosis; effective specific treatment depends of knowing the cause of malabsorption. Antibiotics are advisable in infective cases or case of bacterial overgrowth (short bowel, and stagnant loop). Pancreatic enzymes preparation in pancreatic malabsorption, cholestyramine is useful in cases of malabsorption secondary to bile acid malabsorption. Specific antidiarrheal medications are useful if the mechanism of diarrhoea is identified, an example is clonidine in secretory diarrhoea (Shaffer, and Thomson, 2000)
Prognosis of malabsorption depends on patient factors as age, associated diseases (AIDS, Addisons disease, diabetes), and management factors. Prolonged untreated deficiencies or acute disturbance of electrolytes may seriously affect the disease outcome. Although malabsorption syndrome has high morbidity; yet except cystic fibrosis, it has a low mortality. Another factor is the slowly progressive course and late onset of some disorders, which may delay the treatment. Patient education is of great importance in determining the prognosis, as the treatment may be for long period, dietary supplements and restriction may continue for life; therefore, patient understanding and cooperation is an important factor in prognosis (Semrad, and Powell, 2008).
Conclusion
Malabsorption syndrome is a challenging condition because of the various causes, the patho-physiological mechanisms, and the complex differential diagnosis. Tailoring management strategy based on individual case presentation is the best approach for proper diagnosis and efficient treatment.
References
Adlersberg, D., 1960. Classification of Malabsorption Syndrome: Introductory Remarks. American Journal of Clinical Nutrition, (8), 166.
Binder, H. J. 2005. 275: Disorders of Absorption. In Kasper, D., L., Braunwald, E., Fauci, A., Hauser, S., Longo, D., L., and Jameson, J., L. (editors). Harrisons Principles of Internal Medicine. 16th edition. New York: McGraw-Hill Medical Publishing Division. 3113-3120.
Diakowska, D., Diakowski, W., Knsat, W., Grabowski, K., et al, 2006. Abnormal Metabolism of Cholesterol Fractions in Chronic Pancreatitis and Results after Surgical Treatment. Adv Clin Exp Med, 15 (4), 631-636.
Dutly, F., and Altwegg, M., 2001. Whipples Disease and Tropheryma whippelii . Clinical Microbiology Reviews, 14 (3), 561-583.
Green, P. H. R. and Cellier, C., 2007. Celiac Disease. N Engl J Med, 357 (17), 1731-1743.
Greenson, J. K., 2005. The Surgical Pathology of Malabsorption. Web.
Montalto, M., Santoro, L., DOnofrio, D., Curigliano, V. et al, 2008. Classification of malabsorption syndrome. Dig Dis, 26(2), 104-111.
Parrish, C. R., 2005. The Clinicians Guide to Short Bowel Syndrome. Practical Gastroenterology, 29 (9), 67-106.
Scott, Ronald, B. [Sir] (Editor), 1975. Prices Textbook of the Practice of Medicine. 11th edition. London: Oxford University Press.
Sedlack, E., and Viggiano, T., 2008. Chapter 7: Gastroenterology and Hepatology, Part 1. In Habermann, T. M., and Ghosh, A. K., ed. Mayo Clinic Internal Medicine Concise Textbook. Rochester, MN: Mayo Clinic Scientific Press and Informa Healthcare USA, INC. 228-231.
Semrad, C.E., and Powell, D., W, 2008. Chapter 143: Approach to the Patient with Diarrhea and Malabsorption. In Goldman, L., and Ausiello, D., ed. Cecil Textbook of Medicine. 23. Philadelphia, PA: Saunders. 1046-1062.
Shaffer, E., A., Thomson, A., B., Astra Inc. Staff, and Staff of the Canadian Association of Gastroenterology, 2000. First Principles of Gastroenterology: The Basis of Disease and an Approach to Management. Chapter 7: Section 9. Ottawa: Canadian Public Health Association.
Schiller, L.R., 2004. Chronic Diarrhea. Gastroenterology, (127), 287-293.
Thomas, P. D., Forbes, A., Green, J., Howdle, P., Long, R. et al, 2003. Guidelines for the investigation of chronic diarrhoea, 2nd edition. Gut, (52 [Suppl V]), v1-v15.
Torres, M. I., Casado, M. A. L., and Rios, A., 2007. New aspects in celiac disease. World J Gastroenterol, 13 (8), 1156-1161.
Turnpenny, P., and Ellard, S., 2007. Emerys Elements of Medical Genetics. Section B. London: Elsevier/Churchill Livingstone.
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