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- Chronic diarrhea is defined as stool output >200 g/24 h in children and adults, or 10 g/kg/24 h in infants, that has occurred for >30 days.
- Should be differentiated from acute diarrhea, which is generally caused by enteric pathogens, is self-limiting, and has a duration of symptoms <14 days; as well as persistent diarrhea, which lasts 14 to 29 days
- Gender and genetic factors do not play a significant role in most cases of chronic diarrhea.
- Infectious chronic diarrhea is seen most commonly in low-resource settings.
The two major categories of chronic diarrhea are osmotic and secretory. Inflammatory and motility disorders are important subcategories to consider.
- Osmotic diarrhea occurs when unabsorbable solute accumulates in the lumen of the small intestine and colon, increasing intraluminal osmotic pressure and resulting in excessive fluid and electrolyte losses in stool.
- Osmotic diarrhea will improve with fasting.
- Osmotic diarrhea is usually related to malabsorption of dietary products or to the presence of congenital or acquired disaccharidase deficiency or glucose–galactose defects.
- Secretory diarrhea occurs when the net secretion of fluid and electrolyte is in excess of absorption in the intestine:
- Secretory diarrhea occurs independently of the osmotic load in the intestinal lumen
- Will not improve with fasting
- The mechanisms for secretory diarrhea include the activation of intracellular mediators such as cAMP, cGMP, and calcium-dependent channels.
- These mediators stimulate active chloride secretion from the crypt cells and inhibit the neutral coupled sodium chloride absorption.
- Inflammation in the intestine can cause an alteration in mucosal integrity resulting in exudative loss of mucus, blood, and/or protein. Increased permeability and altered mucosal surface area may affect absorption and result in diarrhea due to malabsorption.
- Motility disorders affect intestinal transit time. Hypomotility can allow stasis from bacterial overgrowth and can lead to diarrhea.