diarrhea

Importance: Chronic diarrhea is defined as loose or watery stools lasting longer than 4 weeks and affects approximately 6% to 7% of adults in the US. More than 90% of patients with chronic diarrhea have a noninfectious etiology.

Observations: The most common causes of chronic, noninfectious diarrhea are irritable bowel syndrome with diarrhea (IBS-D) and functional diarrhea. IBS-D typically presents with recurrent abdominal pain relieved or worsened after defecation. Functional diarrhea is a condition in which more than 25% of bowel movements in the preceding 3 months are loose or watery, but it is not associated with significant abdominal pain. Chronic diarrhea due to a small-bowel source, such as celiac disease or small intestinal bacterial overgrowth, is typically associated with large-volume diarrhea and weight loss, with or without steatorrhea. Celiac disease is an autoimmune condition defined by enteropathy precipitated by exposure to dietary gluten in genetically predisposed individuals, and small intestinal bacterial overgrowth is characterized by excessive bacteria in the small bowel. Chronic diarrhea due to colon pathology, such as bile acid diarrhea and microscopic colitis, typically presents with frequent, low-volume stools, with or without urgency and excess mucus. Bile acid diarrhea is characterized by excess bile acids in the colon, and microscopic colitis is characterized by chronic inflammation on colon biopsies despite normal endoscopic appearance. Evaluation of chronic diarrhea includes serological testing for celiac disease (tissue transglutaminase immunoglobulin A, along with total immunoglobulin A) and stool testing for fecal calprotectin to evaluate for inflammatory bowel disease. Patients with gastrointestinal bleeding, unexplained weight loss, 45 years or older, nocturnal diarrhea, steatorrhea, and/or iron deficiency anemia should undergo colonoscopy to evaluate for colorectal cancer as well as upper endoscopy. During colonoscopy, random biopsies are recommended to evaluate for microscopic colitis, which affects 13% of patients with chronic diarrhea. If evaluation does not identify a cause of chronic diarrhea, likely diagnoses are IBS-D or functional diarrhea and the patient should be treated with lifestyle modification, such as regularly scheduled meals, exercise, intake of at least 8 cups of noncaffeinated fluids daily, limiting caffeine to 3 cups or fewer daily, and avoiding alcohol and carbonated beverages. For general treatment of chronic diarrhea, dietary modifications, such as consuming a diet low in fermentable oligosaccharides (legumes, wheat, onions, garlic), disaccharides (lactose), and monosaccharides (fructose), and polyols (sorbitol, mannitol), or medications, such as opiate agonists (loperamide), anticholinergics (hyoscyamine, dicyclomine), or 5-hydroxytryptamine 3 receptor (5-HT3) antagonists (ondansetron), can be prescribed. These therapies typically improve diarrhea in 50% to 80% of patients.

Conclusions and relevance: The most common causes of chronic, noninfectious diarrhea include IBS-D and functional diarrhea. Diagnostic testing should include consideration of celiac disease, inflammatory bowel disease, and microscopic colitis. Empiric therapies for chronic diarrhea include lifestyle and dietary modifications and medications, including opiate agonists, anticholinergics, and 5-HT3 antagonists.