What are the causes of chronic diarrhea?

From the Guidelines

Chronic diarrhea is a complex condition with numerous potential causes, including inflammatory, infectious, malabsorptive, and medication-related etiologies, and a thorough diagnostic approach is essential to identify the underlying cause and guide treatment. The causes of chronic diarrhea can be categorized into several groups, including:

• Inflammatory conditions, such as inflammatory bowel diseases (Crohn's disease and ulcerative colitis), microscopic colitis, and celiac disease 1
• Infections, particularly in immunocompromised individuals, with pathogens like Giardia, Cryptosporidium, and Clostridioides difficile 1
• Malabsorption syndromes, such as lactose intolerance, pancreatic insufficiency, and bile acid malabsorption 1
• Medication side effects, particularly antibiotics, metformin, NSAIDs, proton pump inhibitors, and certain antihypertensives 1
• Functional disorders, like irritable bowel syndrome, which often presents with chronic diarrhea alternating with constipation 1
• Endocrine disorders, including hyperthyroidism and diabetes, which can disrupt normal bowel function 1
• Neoplastic causes, such as colon cancer and carcinoid syndrome, which should be considered, especially in older adults 1
• Surgical alterations to the digestive tract, including gastric bypass or gallbladder removal, which may result in chronic diarrhea 1

A detailed history and examination are essential in the assessment of patients with chronic diarrhea, including the presence of "alarm features" and the distinction between malabsorptive and colonic/inflammatory forms of diarrhea 1. The diagnostic approach should include a thorough medical history, physical examination, stool studies, blood tests, and potentially endoscopic procedures to identify the underlying cause and guide appropriate treatment 1. The most recent and highest quality study, published in 2018, provides a comprehensive guideline for the investigation of chronic diarrhea in adults, emphasizing the importance of a detailed history and examination, as well as the use of various diagnostic tests to identify the underlying cause 1.

From the Research

Causes of Chronic Diarrhea

• Chronic diarrhea can be caused by a variety of non-infectious factors, including irritable bowel syndrome (IBS), lactose intolerance, dietary factors, inflammatory bowel disease, and colon cancer 2
• Other causes of chronic diarrhea include food intolerances, side effects of drugs, postsurgical conditions, and systemic diseases such as diabetes or hyperthyroidism 3
• Infectious agents can also cause chronic diarrhea, although this is less common in developed countries 4
• Protozoal pathogens, such as Giardia lamblia and Entamoeba histolytica, and bacterial pathogens, such as Tropheryma whipplei, can cause chronic diarrhea 5
• Opportunistic pathogens can cause diarrhea in immunocompromised patients, such as those with HIV 5

Classification of Chronic Diarrhea

• Chronic diarrhea can be classified into different categories, including inflammatory, neoplastic, malabsorptive, infective, vascular, and functional gastrointestinal diseases 3
• The classification of chronic diarrhea is important for determining the underlying cause and guiding treatment 3

Underlying Mechanisms

• Chronic diarrhea can result from decreased absorption of gastrointestinal contents or increased fluid secretion into the bowel 2
• The underlying mechanisms of chronic diarrhea can vary depending on the cause, and treatment should be directed at the underlying cause whenever possible 2