What is the differential diagnosis of chronic diarrhea in immunocompetent patients?

Case series from tertiary-care centers report toddler's diarrhea, cow's milk sensitivity enteropathy, infection, celiac disease, and idiopathic chronic diarrhea as the most common etiologies in the pediatric population. In adults, the most common etiologies were secretory diarrhea (idiopathic, laxative abuse, irritable bowel syndrome, diabetes mellitus, and fecal incontinence), malabsorption (pancreatic disease, noninflammatory short bowel syndrome, postgastrectomy, hyperthyroidism, and cholestasis), microscopic colitis, inflammatory bowel disease, celiac sprue, and radiation colitis. (Grade of recommendation: C, based on case series.