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Chapter 040. Diarrhea and Constipation (Part 8)

SECRETORY CAUSES Secretory diarrheas are due to derangements in fluid and electrolyte transport across the enterocolonic mucosa. They are characterized clinically by watery, large-volume fecal outputs that are typically painless and persist with fasting. Because there is no malabsorbed solute, stool osmolality is accounted for by normal endogenous electrolytes with no fecal osmotic gap. Medications Side effects from regular ingestion of drugs and toxins are the most common secretory causes of chronic diarrhea. Hundreds of prescription and overthe-counter medications (see "Other Causes of Acute Diarrhea," above) may produce unwanted diarrhea. Surreptitious or habitual use of stimulant laxatives [e.g., senna, cascara, bisacodyl,. | Chapter 040. Diarrhea and Constipation Part 8 SECRETORY CAUSES Secretory diarrheas are due to derangements in fluid and electrolyte transport across the enterocolonic mucosa. They are characterized clinically by watery large-volume fecal outputs that are typically painless and persist with fasting. Because there is no malabsorbed solute stool osmolality is accounted for by normal endogenous electrolytes with no fecal osmotic gap. Medications Side effects from regular ingestion of drugs and toxins are the most common secretory causes of chronic diarrhea. Hundreds of prescription and over-the-counter medications see Other Causes of Acute Diarrhea above may produce unwanted diarrhea. Surreptitious or habitual use of stimulant laxatives e.g. senna cascara bisacodyl ricinoleic acid castor oil must also be considered. Chronic ethanol consumption may cause a secretory-type diarrhea due to enterocyte injury with impaired sodium and water absorption as well as rapid transit and other alterations. Inadvertent ingestion of certain environmental toxins e.g. arsenic may lead to chronic rather than acute forms of diarrhea. Certain bacterial infections may occasionally persist and be associated with a secretory-type diarrhea. Bowel Resection Mucosal Disease or Enterocolic Fistula These conditions may result in a secretory-type diarrhea because of inadequate surface for reabsorption of secreted fluids and electrolytes. Unlike other secretory diarrheas this subset of conditions tends to worsen with eating. With disease e.g. Crohn s ileitis or resection of 100 cm of terminal ileum dihydroxy bile acids may escape absorption and stimulate colonic secretion cholorrheic diarrhea . This mechanism may contribute to so-called idiopathic secretory diarrhea in which bile acids are functionally malabsorbed from a normal-appearing terminal ileum. Partial bowel obstruction ostomy stricture or fecal impaction may paradoxically lead to increased fecal output due to fluid hypersecretion. Hormones