Diseases Producing Malabsorption and Maldigestion

Malabsorption refers to the impaired intestinal absorption of nutrients. It can result from congenital defects in absorption and the transport of ions and nutrients, defects in hydrolysis within the intestinal lumen, acquired defects in the intestinal absorptive cells that line the surface of the intestine, impaired bile production, or interruption of enterohepatic circulation or secondary to pancreatic insufficiency. Maldigestion, another factor in nutrient absorption, refers to the impaired digestion of nutrients within the intestinal lumen or at the terminal digestive site of the brush border membrane of mucosal epithelial cells. Although malabsorption and maldigestion are pathophysiologically distinct, they are interdependent, and in clinical practice, malabsorption has come to signify derangements in either or both processes. This chapter discusses the clinical manifestations of malabsorption and tests for suspected malabsorption. The diseases that can cause malabsorption, their diagnosis, and treatment recommendations are included. Figures illustrate the diagnosis and management of celiac disease; an approach to gluten challenge for the diagnosis or exclusion of celiac disease in patients maintained on a gluten-free diet without previous definitive diagnostic testing; and the histologic features of celiac disease, Crohn disease, collagenous sprue, autoimmune enteropathy, eosinophilic gastritis, and intestinal lymphangiectasia.  This review contains 9 figures, 25 tables, and 116 references. Keywords: Malabsorption, maldigestion, Crohn disease, celiac disease, tropical sprue, diarrhea, endoscopy, short bowel syndrome, bacterial overgrowth