Bile Acid Insufficiency

Pathogenesis

Insufficient bile acids can result from a disorder at any step in the enterohepatic circulation of bile acids. In severe intrinsic liver disease, the liver may not produce enough bile acids; in partial biliary obstruction, the bile acids do not reach the intestinal lumen in sufficient concentration; in bacterial overgrowth of the small intestine, bile acids are deconjugated before they can participate in fat absorption; and in disorders of the terminal ileum, bile acids are not reabsorbed adequately to maintain the bile acid pool.

Because bile acids facilitate the absorption of dietary fat by the formation of intraluminal micelles, a deficiency in bile acids results in malabsorption of fat. Absorption of protein and carbohydrate is normal.

Diagnosis

The upper gastrointestinal and small-bowel x-ray series usually are normal in bile acid insufficiency, unless the results suggest a lesion that obstructs the common bile duct; small-bowel stasis or diverticula, which may allow bacterial overgrowth; or terminal ileal disease. Because bile acids facilitate but are not necessary for fat absorption, steatorrhea usually does not exceed 20 g per 24 hours. The bile acid breath test is abnormal if bacterial overgrowth or terminal ileal disease is present. A normal xylose tolerance test and a normal small-bowel biopsy are expected unless there is bacterial overgrowth. Bacterial overgrowth and disease of the terminal ileum also may cause abnormal results on the Schilling test.

Treatment

The treatment of bile acid insufficiency varies with the cause. Improvement in the liver disease or relief of the biliary obstruction may be adequate.

Small-bowel bacterial overgrowth

Patients who have small-bowel bacterial overgrowth may respond to the administration of metronidazole or tetracycline or another broad-spectrum antibiotic for 1 or more weeks. If bile acid deficiency is not correctable, a reduction in dietary long-chain triglycerides is indicated. Medium-chain triglycerides, which do not require bile acids for absorption, can be used to supplement dietary fat. Additional fat-soluble vitamins may be indicated.

Terminal ileal disorders

Patients who have disorders of the terminal ileum may have malabsorption of vitamin B₁₂ and of bile acids. An abnormal Schilling test in these patients indicates that they should receive monthly injections of vitamin B₁₂. When disease of the terminal ileum impairs bile acid absorption, the bile acids pass into the colon, where unconjugated dihydroxy bile acids inhibit the absorption of water and electrolytes. Thus, these patients may have both steatorrhea as a result of bile acid deficiency and watery diarrhea from the effects of bile acids on the colon. More extensive disease or resection of the terminal ileum predisposes to greater reductions in the bile acid pool, and steatorrhea predominates. In patients with lesser involvement, watery diarrhea is prominent, and steatorrhea may not be clinically evident.

Cholestyramine

Cholestyramine, which binds bile acids, may be taken orally to treat the watery diarrhea in patients who have less extensive disease or small resections. The dosage ranges from one-half packet (2 g) once or twice a day to several packets a day with meals. Because bound bile acids do not participate in fat absorption, the steatorrhea may actually worsen. In patients with little involvement of the terminal ileum, however, the net effect may be an improvement in the diarrhea. In patients with more extensive involvement in whom steatorrhea is aggravated by cholestyramine, supplemental medium-chain triglycerides may be necessary. Nearly all patients benefit from restriction of long-chain triglycerides (i.e., ordinary dietary fat).

Jennifer Bowles

Jennifer is a clinical pharmacologist. She helps doctors of all medical specialties choose medications. Jennifer consults about drug dosage, interactions, and side effects.