Osmotic diarrhea occurs after malabsorption of aningested substance, which “pulls” water into the bowellumen. A classic example is the diarrhea of lactose intolerance. Osmotic diarrhea also can result from generalizedmaldigestion, such as that seen with pancreatic insufficiency or with intestinal injury. Certain nonabsorbable laxatives, such as polyethylene glycol and milk of magnesia,also cause osmotic diarrhea. Fermentation of malabsorbed substances (e.g., lactose) often occurs, resulting in gas,cramps, and acidic stools. A common cause of chronic loosestools in early childhood is functional diarrhea, commonly known as toddler’s diarrhea. This condition is defined byfrequent watery stools in the setting of normal growth and
Common Gastroenteritis* Gastroenteritis* Gastroenteritis* Systemic infection Food poisoning Food poisoning Antibiotic associated (?) Systemic infection Antibiotic associated Antibiotic associated
Common Postinfectious secondary lactase deficiency Cow’s milk/soy protein intolerance Chronic nonspecific diarrhea of infancy (toddler’s diarrhea) Celiac disease Cystic fibrosis AIDS enteropathy Postinfectious secondary lactase deficiency Irritable bowel syndrome Celiac disease Lactose intolerance Giardiasis Inflammatory bowel disease Irritable bowel syndrome Inflammatory bowel disease Lactose intolerance Giardiasis Laxative abuse (anorexia nervosa) Celiac disease
Rare Primary immune defects Familial villous atrophy (?) Secretory tumors Congenital chloridorrhea Acrodermatitis enteropathica Lymphangiectasia Abetalipoproteinemia Eosinophilic gastroenteritis Short bowel syndrome Intractable diarrhea syndrome Autoimmune enteropathy Factitious Acquired immune defects Secretory tumors Secretory tumor Primary bowel tumor Pseudo-obstruction AIDS enteropathy Factitious AIDS enteropathy
AIDS, Acquired immunodeficiency syndrome.
*Gastroenteritis includes viral (rotavirus, norovirus, astrovirus) and bacterial (Salmonella, Shigella, Escherichia coli, Clostridium difficile, Yersinia, Campylobacter, other) agents.
weight gain and is caused by excessive intake of sweetened liquids, overwhelming the disaccharide absorptive capacityof the intestine. Diarrhea typically improves tremendouslywhen the child’s beverage intake is reduced or changed.
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Stools are isosmotic, even in osmotic diarrhea, because of the relatively free exchange of water across the intestinalmucosa. Osmoles present in the stool are a mixture of electrolytes and other osmotically active solutes. To determinewhether the diarrhea is osmotic or secretory, the osmotic gap is calculated:
Assuming the stool is isosmotic (an osmolarity of 290 mOs-m/L), the measured stool sodium and potassium (and their associated anions, accounting for an equal amount) accounts for much of the osmolality. Secretory diarrhea is characterized by an osmotic gap of less than 50. A number significantly higher than 50 defines osmotic diarrhea and indicates that malabsorbed substances other than electrolytes account for fecal osmolarity.