Crohns disease typically affects fairly well demarcated segments of bowel in the colon and often affects the end of the small bowel. Irritable bowel syndrome
Another possible cause of diarrhea is irritable bowel syndrome (IBS), which usually presents with abdominal discomfort relieved by defecation and unusual stool (diarrhea or constipation) for at least three days a week over the previous three months. Symptoms of diarrhea-predominant IBS can be managed through a combination of dietary changes, soluble fiber supplements and medications such as loperamide or codeine. About 30% of patients with diarrhea-predominant IBS have bile acid malabsorption diagnosed with an abnormal SeHCAT test. Other diseases
Diarrhea can be caused by other diseases and conditions, namely:

Chronic ethanol ingestion
Hyperthyroidism
Certain medications
Bile acid malabsorption
Ischemic bowel disease: This usually affects older people and can be due to blocked arteries. Microscopic colitis, a type of inflammatory bowel disease where changes are seen only on histological examination of colonic biopsies. Bile salt malabsorption (primary bile acid diarrhea) where excessive bile acids in the colon produce a secretory diarrhea. Hormone-secreting tumors: some hormones, e.g. serotonin, can cause diarrhea if secreted in excess (usually from a tumor). Chronic mild diarrhea in infants and toddlers may occur with no obvious cause and with no other ill effects; this condition is called toddlers diarrhea. Environmental enteropathy
Radiation enteropathy following treatment for pelvic and abdominal cancers. Medications
Some medications, such as the penicillin can cause diarrhea. Over 700 medications are known to cause diarrhea.
Non-steroidal anti-inflammatory drugs (NSAIDs) have also been used. Hydroxychloroquine has proven effective in some cases. History
In a 1985 paper published in the Journal of the American Medical Association, McCarty and colleagues first described a case series of patients with this disorder, for which they coined the abbreviation RS3PE. RS3PE was initially thought to represent a form of seronegative rheumatoid arthritis but is now believed to be a separate syndrome. == References ==