Another way to differentiate between osmotic and secretory diarrhea is to stop all feedings (in hospitalized patientsreceiving intravenous fluids). If the diarrhea stops completely while the child is NPO (nothing by mouth), thepatient has osmotic diarrhea. A child with a pure secretory diarrhea would continue to have massive stool output.Neither method for classifying diarrhea works perfectly,because most diarrheal illnesses are a mixture of secretoryand osmotic components. Viral enteritis damages the intestinal lining, causing malabsorption and osmotic diarrhea. Theassociated inflammation results in release of mediators that cause excessive secretion. A child with viral enteritis mayhave decreased stool volume while NPO, but the secretorycomponent of the diarrhea persists until the inflammationresolves.
The history should include the onset of diarrhea, number and character of stools, estimates of stool volume, and presence of other symptoms, such as blood in the stool, fever, and weight loss. Recent travel and exposures should be documented, dietary factors should be investigated, and a list of medications recently used should be obtained. Factors that seem to worsen or improve the diarrhea should be determined. Physical examination should be thorough, evaluating for abdominal distention, tenderness, quality of bowel sounds, presence of blood in the stool or a large fecal mass on rectal examination, and anal sphincter tone.
Laboratory testing should include stool culture and complete blood count if bacterial enteritis is suspected. If diarrhea occurs after a course of antibiotics, a Clostridium difficile toxin assay should be ordered; if stools are reported to be oily orfatty, fecal fat content or fecal elastase to test for pancreatic insufficiency should be measured. Tests for specific diagnosesshould be sent when appropriate (e.g., serum antibody testsfor celiac disease; colonoscopy for suspected ulcerative colitis). A trial of lactose restriction for several days or lactosebreath hydrogen testing is helpful in the evaluation of lactoseintolerance.
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Constipation is a common problem in childhood. When a child is thought to be constipated, his parents may be concerned about straining with defecation, hard stool consistency, large stool size, decreased stool frequency, fear of passing stools, or any combination of these. Physicians define constipation as two or fewer stools per week or passage of hard, pellet-like stools for at least 2 weeks. A common pattern of constipation is functional constipation, which is characterized by two or fewer stools per week, voluntary withholding of stool, and infrequent passage of large-diameter, often painful stools. Children with functional fecal retention often exhibit “retentive posturing” (standing or sitting with legs extended and stiffor crossed legs) and have associated fecal incontinence caused by leakage of retained stool (encopresis).
The differential diagnosis is listed in Table 126-10. Functional constipation commonly occurs during toilet training, when the child is unwilling to defecate on the toilet. Retained stool becomes harder and larger over time, leading to painful defecation. This aggravates voluntary withholding of stool, with perpetuation of the constipation.