hello welcome to hcm well there are a large number of underlying conditions/disease which can cause chronic diarrhoea,below i am mentioning the list of such conditions/diseases--- (1) INTESTINAL INFECTIONS - (a) bacterial infections such as - typhoid - cholera (b) protozoal infections such as - intestinal amoebiasis caused by organism called as entamoeba histolytica - giardiasis - helminthiasis (c) viral infections such as - rotavirus - HIV - hepatitis virus specially hepatitis A and E (d) rarely,some fungal infections can also lead to chronic diarrhoea (2) IRRITABLE BOWEL SYNDROME - it is one of the most common cause of chronic diarrhoea (3) INFLAMMATORY BOWEL DISEASE it includes maily these 2 conditions (a) ulcerative colitis (b) crohns disease (4) ENDOCRINE / HORMONAL DISORDERS - includes - diabetes mellitus - thyroid disease specifically hyperthyroidism - pheochromocytoma - zollinger ellison syndrome - addisons disease (5) ALLERGY TO CERTAIN FOODS - - celiac disease - intolerance to lactose - artificial sweeteners (6) CANCER OF THE GASTRO-INTESTINAL TRACT - such as - carcinoids - polyps in majority of the cases a doctor is usually able to diagnose the underlying cause of chronic diarrhoea by evaluating the detailed clinical history , dietary habbits , presence of certain specific signs and symptoms , characteristics of the stools and performing a physical examination but in some cases it may require to do certain tests and lab investigations to make a precise and conclusive diagnosis by identifying the underlying cause of chronic diarrhoea....tests which may be required are ---- (1) certain specific blood tests like WIDAL test for typhoid , antibody detection for autoimmune diseases (2) stool examination for microbiology and for detection of any ova/cysts in case of suspected parasitic infections (3) breath test (4) colonoscopy and sigmoidoscopy (5) scans like CT scan and MRI TREATMENT depend on the underlying cause and is aimed at removing the underlying cause which is causing chronic diarrhoea... i hope you will find the information above to be very useful regards HCM