eMedicine Specialties > Gastroenterology > Systemic Disease

Malabsorption

Author: Jan-Michael A Klapproth, MD, Assistant Professor, Department of Medicine, Division of Digestive Diseases, Emory University School of Medicine
Coauthor(s): Vincent W Yang, MD, PhD, R Bruce Logue Professor, Director, Division of Digestive Diseases, Department of Medicine, Professor of Hematology and Oncology, Winship Cancer Institute, Emory University School of Medicine
Contributor Information and Disclosures

Updated: Aug 14, 2008

Introduction

Background

Malabsorption is a clinical term that encompasses defects occurring during the digestion and absorption of food nutrients by and infections of the gastrointestinal tract. The digestion or absorption of a single nutrient component may be impaired, as in lactose intolerance due to lactase deficiency. When a diffuse disorder, such as celiac disease or Crohn's disease, affects the intestine, the absorption of almost all nutrients is impaired.

While presenting symptoms, such as diarrhea and weight loss, may be common, the specific causes of malabsorption are usually established based on physiological evaluations. The treatment often depends on the establishment of a definitive etiology for malabsorption.

Pathophysiology

To understand the mechanisms of malabsorption, understanding the normal physiological process of digestion and absorption by the intestinal tract is necessary.
 
In general, the digestion and absorption of food materials can be divided into 3 major phases: luminal, mucosal, and postabsorptive. The luminal phase is the phase in which dietary fats, proteins, and carbohydrates are hydrolyzed and solubilized by secreted digestive enzymes and bile. The mucosal phase relies on the integrity of the brush-border membrane of intestinal epithelial cells to transport digested products from the lumen into the cells. In the postabsorptive phase, reassembled lipids and other key nutrients are transported via lymphatics and portal circulation from epithelial cells to other parts of the body.

Perturbation by disease processes in any of these phases frequently results in malabsorption.

Clinical

History

The osmotic load resulting from the inability of the intestine to absorb certain nutrient elements causes the presenting symptoms. On occasion, the products of digestion produced by bacterial flora also result in a secretory reaction by the intestine.

• Diarrhea
  • Diarrhea is the most common symptomatic complaint.
  • Diarrhea frequently is watery, reflecting the osmotic load received by the intestine.
  • Bacterial action producing hydroxy fatty acids from undigested fat also can increase net fluid secretion from the intestine, further worsening the diarrhea.
• Steatorrhea
  • Steatorrhea is the result of fat malabsorption.
  • The hallmark of steatorrhea is the passage of pale, bulky, and malodorous stools.
  • Such stools often float on top of the toilet water and are difficult to flush. Also, patients find floating oil droplets in the toilet following defecation.
• Weight loss and fatigue
  • Weight loss is common and may be pronounced; however, patients may compensate by increasing their caloric consumption, masking weight loss from malabsorption.
  • The chance of weight loss increases in diffuse diseases involving the intestine, such as celiac disease and Whipple disease.
• Flatulence and abdominal distention
  • Bacterial fermentation of unabsorbed food substances releases gaseous products, such as hydrogen and methane, causing flatulence.
  • Flatulence often causes uncomfortable abdominal distention and cramps.
• Edema
  • Hypoalbuminemia from chronic protein malabsorption or from loss of protein into the intestinal lumen causes peripheral edema.
  • Extensive obstruction of the lymphatic system, as seen in intestinal lymphangiectasia, can cause protein loss.
  • With severe protein depletion, ascites may develop.
• Anemia
  • Depending on the cause, anemia resulting from malabsorption can be either microcytic (iron deficiency) or macrocytic (vitamin B-12 deficiency).
  • Iron deficiency anemia often is a manifestation of celiac disease.
  • Ileal involvement in Crohn disease or ileal resection can cause megaloblastic anemia due to vitamin B-12 deficiency.
• Bleeding disorders
  • Bleeding usually is a consequence of vitamin K malabsorption and subsequent hypoprothrombinemia.
  • Ecchymosis usually is the manifesting symptom, although, occasionally, melena and hematuria occur.
• Metabolic defects of bones
  • Vitamin D deficiency can cause bone disorders, such as osteopenia or osteomalacia.
  • Bone pain and pathological fractures may be observed.
  • Malabsorption of calcium can lead to secondary hyperparathyroidism.
• Neurological manifestations
  • Electrolyte disturbances, such as hypocalcemia and hypomagnesemia, can lead to tetany, manifesting as the Trousseau sign and the Chvostek sign.
  • Vitamin malabsorption can cause generalized motor weakness (pantothenic acid, vitamin D) or peripheral neuropathy (thiamine), a sense of loss for vibration and position (cobalamin), night blindness (vitamin A), and seizures (biotin).

See related CME at Efficient Diagnosis of Suspected Functional Bowel Disorders.

Physical

• General physical examination
  • Patients may have orthostatic hypotension.
  • Patients may complain of fatigue.
  • Signs of weight loss, muscle wasting, or both may be present.
  • Patients may have signs of loss of subcutaneous fat.
• Abdominal examination
  • The abdomen may be distended, and bowel sounds may be hyperactive.
  • Ascites may be present in severe hypoproteinemia.
• Dermatological manifestations
  • Pale skin may reveal anemia.
  • Ecchymoses due to vitamin K deficiency may be present.
  • Dermatitis herpetiformis, erythema nodosum, and pyoderma gangrenosum may be present.
  • Pellagra, alopecia, or seborrheic dermatitis may be present.
• Neurological examination
  • Motor weakness, peripheral neuropathy, or ataxia may be present.
  • The Chvostek sign or the Trousseau sign may be evident due to hypocalcemia or hypomagnesemia.
• Cheilosis, glossitis, or aphthous ulcers of the mouth
• Peripheral edema

Causes

The best way to classify the numerous causes of malabsorption is to consider the 3 phases of digestion and absorption.

• Luminal phase
  • Impaired nutrient hydrolysis
    • The most common cause for impaired nutrient hydrolysis is pancreatic insufficiency due to chronic pancreatitis, pancreatic resection, pancreatic cancer, or cystic fibrosis. The resultant deficiencies in lipase and proteases lead to lipid and protein malabsorption, respectively.
    • Inactivation of pancreatic enzymes by gastric hypersecretion, as seen in Zollinger-Ellison syndrome, is another cause.
    • Inadequate mixing of nutrients, bile, and pancreatic enzymes, as seen in rapid intestinal transit, gastrojejunostomy, total and partial gastrectomy, or intestinal resection after mesenteric emboli or thrombosis, also causes impaired hydrolysis.
    • Rarely, a failure to convert a proenzyme to active form, such as enterokinase and trypsinogen deficiencies, also can cause protein maldigestion and malabsorption.
  • Impaired micelle formation
    • Impaired micelle formation causes a problem in fat solubilization and subsequent fat malabsorption. This impairment is due to different reasons, including (1) decreased bile salt synthesis from severe parenchymal liver disease (eg, cirrhosis); (2) impaired bile secretion from biliary obstruction or cholestatic jaundice (eg, primary biliary cirrhosis, primary sclerosing cholangitis); (3) impaired enterohepatic bile circulation, as seen in small bowel resection or regional enteritis; or (4) bile salt deconjugation due to small bowel bacterial overgrowth.
    • Stasis of intestinal content caused by a motor abnormality (eg, scleroderma, diabetic neuropathy, intestinal obstruction), an anatomical abnormality (eg, small bowel diverticula, stricture, ischemia, blind loops), or small bowel contamination from enterocolonic fistulas can cause bacterial overgrowth.
  • Luminal availability and processing
    • Luminal bacterial overgrowth can cause a decrease in the availability of substrates, including carbohydrates, proteins, and vitamins (eg, vitamin B-12, folate).
    • Vitamin B-12 deficiency due to pernicious anemia is caused by a lack of intrinsic factor and by pancreatic enzyme deficiency.
• Mucosal phase
  • Impaired brush-border hydrolase activity
    • Disaccharidase deficiency can lead to disaccharide malabsorption.
    • Lactase deficiency, either primary or secondary, is the most common form of disaccharidase deficiency. Genetic factors determine primary lactase deficiency. Secondary lactase deficiency can be due to acute gastroenteritis (rotavirus and giardia infection), chronic alcoholism, celiac sprue, radiation enteritis, regional enteritis, or AIDS enteropathy.
    • Immunoglobulin A (IgA) deficiency (most common immunodeficiency) is due to decreased or absent serum and intestinal IgA, which clinically appears similar to celiac disease and is unresponsive to a gluten-free diet.
    • Acrodermatitis enteropathica is an autosomal recessive disease with selective inability to absorb zinc, leading to villous atrophy and acral dermatitis.
    • Autoimmune enteropathy primarily diagnosed in children presenting with intractable secretory diarrhea and villous atrophy. Autoimmune enteropathy is due to antibodies directed against intestinal epithelial and goblet cells. Additional cell types affected by autoantibodies include islet and parietal cells.
    • Other carbohydrase deficiencies, such as sucrase-isomaltase deficiency, may be the cause.
  • Impaired nutrient absorption
    • Nutrient malabsorption is due to inherited or acquired defects.
    • Inherited defects include glucose-galactose malabsorption, abetalipoproteinemia, cystinuria, and Hartnup disease.
    • Acquired disorders are far more common and are caused by the following: (1) decreased absorptive surface area, as seen in intestinal resection of intestinal bypass; (2) damaged absorbing surface, as seen in celiac sprue, tropical sprue, Crohn's disease, AIDS enteropathy, chemotherapy, or radiation therapy; (3) infiltrating disease of the intestinal wall, such as lymphoma and amyloidosis; and (4) infections, including bacterial overgrowth, giardiasis, Whipple's disease, cryptosporidiosis, and microsporidiosis.
• Postabsorptive phase: Obstruction of the lymphatic system, both congenital (eg, intestinal lymphangiectasia, Milroy disease) and acquired (eg, Whipple disease, neoplasm [including lymphoma], tuberculosis), impairs the absorption of chylomicrons and lipoproteins and may cause fat malabsorption or a protein-losing enteropathy.

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