Chronic Diarrhea in Adults: Evaluation and Differential Diagnosis

Chronic diarrhea is defined as a predominantly loose stool lasting longer than four weeks. A patient history and physical examination with a complete blood count, C-reactive protein, anti-tissue transglutaminase immunoglobulin A (IgA), total IgA, and a basic metabolic panel are useful to evaluate for pathologies such as celiac disease or inflammatory bowel disease. More targeted testing should be based on the differential diagnosis. When the differential diagnosis is broad, stool studies should be used to categorize diarrhea as watery, fatty, or inflammatory. Some disorders can cause more than one type of diarrhea. Watery diarrhea includes secretory, osmotic, and functional types. Functional disorders such as irritable bowel syndrome and functional diarrhea are common causes of chronic diarrhea. Secretory diarrhea can be caused by bile acid malabsorption, microscopic colitis, endocrine disorders, and some postsurgical states. Osmotic diarrhea can present with carbohydrate malabsorption syndromes and laxative abuse. Fatty diarrhea can be caused by malabsorption or maldigestion and includes disorders such as celiac disease, giardiasis, and pancreatic exocrine insufficiency. Inflammatory diarrhea warrants further evaluation and can be caused by disorders such as inflammatory bowel disease, Clostridioides difficile, colitis, and colorectal cancer.