Malabsorption bile salt

This section includes a discussion of celiac disease, disac-charidase deficiency, bacterial overgrowth, bile salt malabsorption, and protein-losing enteropathy and the main laboratory investigations associated with their diagnosis. 

Bile acid malabsorption leading to chronic diarrhea occurs when there is ileal disease (e.g., Crohn s disease), or after resection of the terminal deum it may also occur following cholecystectomy and in some patients with irritable bowel syndromed The malabsorption of bile salts produces diarrhea by two different mechanisms. When significant bile salt depletion occurs, the deficiency of intraluminal bile salts leads to fat malabsorption and steatorrhea. More commonly, malabsorption of bile salts in the ileum leads to increased concentrations of bile salts in the colon where they alter water and electrolyte absorption. This leads to net secretion of water into the lumen and diarrhea. Bile salt malabsorption is probably an underdiagnosed condition and should be suspected in patients with unexplained chronic diarrhea. 

With the growing awareness of the likely role of bile salt malabsorption in the chronic diarrhea of a proportion of... 

Bile salt malabsorption Disaccharidase deficiency Small bowel bacterial overgrowth Mesenteric ischemia Radiation enteritis Lymphoma... 

Gallstones occur commonly in patients with Crohn s disease (particularly with terminal ileal disease) and may be related to bile salt malabsorption. Also, cholangiocarcinoma occurs 10 to 20 times more frequently in IBD patients as compared to the general population. ... 

Clinical stresses which interfere with vitamin metabohsm, can result in calcium deficiency leading to osteomalacia and osteoporosis (secondary vitamin D deficiency). These stresses include intestinal malabsorption (lack of bile salts) stomach bypass surgery obstmctive jaundice alcoholism Hver or kidney failure decreasing hydroxylation of vitamin to active forms inborn error of metabohsm and use of anticonverdiants that may lead to increased requirement. 

Small, D. M. Point mutations in the ileal bile salt transporter cause leaks in the enterohepatic circulation leading to severe chronic diarrhea and malabsorption. J. Clin. Invest. 1997,... 

Bile salt deficiency must also be directly studied. It may occur in the absence of obstruction or obvious liver disease (R7). The majority of patients with one form or another of the sprue syndrome will be found to have pancreatic enzymes and bile salts within the normal range. Pancreatic enzymes are absent or markedly deficient in patients with pancreatogenous malabsorption syndrome (B17, F13). It is surprising how frequently this necessary step in differential diagnosis is omitted. 

Severe Ileal disease leading to malabsorption of bile salts. 

The answer is B. This patient s greasy, foul-smelling stools indicate steatorrhea. Her vision problems may be a manifestation of vitamin A deficiency due to fat malabsorption. The most likely explanation is biliary insufficiency, ie, decreased bile salt production leading to poor emulsification of dietary fats. Active ileal disease is a possibility, but the WBC count would likely be elevated unless her condition was in remission. Infection with Giardia is less likely due to the absence of pathogenic organisms in her stool. Lactose intolerance can produce diarrhea but not steatorrhea. 

If more cholesterol enters the bile than can be solubilized by the available bile salts and phosphatidylcholine, cholesterol gallstone disease (cholelithiasis) can occur. This is generally caused by gross malabsorption of bile acids from the intestine, obstruction of the biliary tract, or severe hepatic dysfunction, leading to abnormalities in bile or bile salt production. 

Conjugated bile salts are normally absorbed in the terminal ileum. Disease of the terminal ileum (eg, Crohn s disease) or surgical resection leads to malabsorption of bile salts, which may cause colonic secretory diarrhea. The bile salt binding resins cholestyramine or colestipol may decrease diarrhea caused by excess fecal bile acids (see Chapter 35 Agents Used in Hyperlipidemia). The usual dose is 4-5 g one to three times daily before meals. Side effects include bloating, flatulence, constipation, and fecal impaction. In patients with diminished circulating bile acid pools, further removal of bile acids may lead to an exacerbation of fat malabsorption. These agents bind a number... 

Normally there is very little fat in the feces. However, fat content in stools may increase because of various fat malabsorption syndromes. Such increased fat excretion is steatorrhea. Decreased fat absorption may be the result of failure to emulsify food contents because of a deficiency in bile salts, as in liver disease or bile duct obstruction (stone or tumor). Pancreatic insufficiency may result in an inadequate pancreatic lipase supply. Finally, absorption itself may be faulty because of damage to intestinal mucosal cells through allergy or infection. An example of allergy-based malabsorption is celiac disease, which is usually associated with gluten intolerance. Gluten is a wheat protein. An example of intestinal infection is tropical sprue, which is often curable with tetracycline. Various vitamin deficiencies may accompany fat malabsorption syndromes. 

Malabsorption is defined as an inadequate assimilation of dietary substances due to defects in digestion, absorption or transport. Malabsorption can affect macronutrients (proteins, carbohydrates, fats), micronutrients (vitamins, minerals) or both, causing excessive faecal excretion and producing nutritional deficiencies and GI symptoms. Digestion and absorption occur in three phases, namely (i) the intra-lumen hydrolysis of fats, proteins and carbohydrates by enzymes, and emulsification by bile salts, (ii) digestion by brush-border enzymes and uptake of end-products and (iii) lymphatic transport of nutrients. Malabsorption can occur when any of these phases is impaired. 

Malabsorption has many causes. Some malabsorptive disorders, for example coeliac sprue, impair the absorption of most nutrients, vitamins and trace minerals (global malabsorption) others, for example pernicious anaemia, are more selective. Pancreatic insufficiency causes malabsorption if >90% of function is lost. Increased lumen acidity (e.g. Zollinger-Ellison syndrome) inhibits lipase and fat digestion. Cirrhosis and cholestasis reduce hepatic bile synthesis or delivery of bile salts to the duodenum, causing malabsorption. Some causes are summarised in Table 4.2. 

Naturally occurring vitamin K is absorbed from the intestines only in the presence of bile salts and other lipids through interaction with chylomicrons. Therefore, fat malabsorptive diseases can result in vitamin K deficiency. 

Several diseases, called malabsorption syndromes, result in the lack of absorption of a number of nutrients. Their consequent loss in the feces dearly is not desirable. Malabsorption of lipids, which occurs more frequently than malabsorption of any other class of nutrient, can result in diarrhea and steatorrhea. Steatorrhea, production of feces with a high fat content, derives its name from "stearic add," a fatt> acid, With severe steatorrhea, over 30 g fat may appear in the feces per day. The problem can be elicited by liver diseases that piev ent the pn>duction of bile salts and thus impair the absorption of fats. 

Fal malabsorption syndromes Fat malabsorption syndromes such as cystic fibrosis and cholestatic liver diseases (lack of bile salts) can impair the absorption of vitamin D. 

Blockage of the bile duct caused by problems such as cholesterol-containing gallstones or duodenal or pancreatic tumors can lead to an inadequate concentration of bile salts in the intestine. Digestion and absorption of dietary lipids is diminished. Certain diseases that affect the pancreas can lead to a decrease in bicarbonate and digestive enzymes in the intestinal lumen. (Bicarbonate is required to raise the intestinal pH so that bile salts and digestive enzymes can function.) If dietary fats are not adequately digested, steatorrhea may result. Malabsorption of fats can lead to caloric deficiencies and lack of fat-soluble vitamins and essential fatty acids. 

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