One of the major jobs of the colon is to recycle water for the body. When the entire colon is present and healthy the stools have only enough water in them to remain soft and easy to pass, but not so watery or loose that leakage occurs and dehydration ensues. When a large part of the colon is removed or when the colon is significantly injured the stools are very watery and frequent.

Inflammation is the body’s response to infection or suspected attack or irritation. Inflammation of a body area is labeled by adding the suffix “-itis” to the body part, hence tonsillitis when tonsils are inflamed and appendicitis when the appendix is inflamed. Recognized since ancient times, inflammation has been classically described by the presence of signs and symptoms of redness (rubor), pain (dolar), heat (calor), swelling (tumor) and impairment of the function of the involved organ or tissue. If you have arthritis, joint inflammation; the joint is red, swollen, painful, warm and is stiff, preventing normal function.

Colitis is the term for inflammation of the colon or large bowel or intestine. The rectum is the very last part of the colon. When it is inflamed the term proctitis is used. The colon can be visibly inflamed or it can be inflammed only at the microscopic level, also known as microscopic colitis. When visually inflammed the colon looks irritated on the surface and this can be seen when examining the colon using an endoscope during colonscopy or sigmoidoscopy. When it is microscopically inflammed, the surface appears normal or minimally irritated but under the microscope the lining examined from biopsies shows excess inflammation cells or other changes or irritation and injury.

In colitis the colon is usually quite red and swollen appearing when seen by colonoscopy (scope exam of the colon) except when the inflammation is only microscopic. The surface is often ulerated or eroded. Abdominal pain and impaired function occurs resulting in diarrhea because the damaged colon loses some of its ability to absorb water. If enough damage occurs to the lining sloughing of the surface cells occurs with passage of bloody stools, mucus, and even the appearance of tissue.

Inflammation has cell and fluid components. The cell component includes various white blood cells. The type of white blood cells found in the lining of the intestine determines the cause and effect on the intestine. Fluids include chemicals secreted to fight infection or presumed infection that can cause damage to the colon lining.

Colitis can be acute (self-limited) like E. coli infection or chronic like in ulcerative colitis. Causes of colitis include infections, ischemia (poor blood flow), food allergies, food protein intolerances, lack of normal bacterial flora or stool (after antibiotics, diversion after a colostomy), radiation injury, chemotherapy induced low white blood cell counts (neutropenic), or idiopathic (unknown cause).

Chronic colitis is one of several types of inflammatory bowel disorders or IBD for short and should not be confused with IBS the term for irritable bowel syndrome. Irritable bowel syndrome (IBS) does not involve any colon inflammation though it was referred to in the past as mucus colitis because of common symptom of excess mucus in stools or spastic colitis because of the common complaint of painful spasms of the colon that commonly occur in IBS. Biopsies of colon tissue in irritable bowel syndrome are by definition normal, that is, do not show signs of inflammation therefore IBS historically has not been been considered an inflammatory bowel disorder. However, newer information, including the discovery of mastocytic enterocolitis (see separate page describing this condition) have raised the question about IBS being a form of IBD, at least in some types of IBS.

When infectious colitis is severe with bloody diarrhea, fever and chills it is typically called dysentery. The bacteria that cause acute infectious colitis include Escherichia coli, Salmonella, Shigella, Yesinia enterocolitica, Campylobacter jejuni, Mycobacterium tuberculosis (TB), Vibrio parahemolyticus and Clostridium difficile.  Escherichia coli is normally present in stool but not in strains that have a toxic protein or invades the colon lining. Clostridrium difficile also is normally present in low levels in most people’s stool but becomes dominant and starts secreting a toxin that damages the intestine after broad spectrum antibiotics kill off the other bacteria in the intestine. Parasites that can cause acute infectious colitis include Entamoeba histolytica (Amebic dysentery), Schistosoma bacteria, Balantidum coli, and Trichinalis spiralis (pork ingestion). The virus most commonly causing colitis is Cytomegalovirus virus but in setting of poor immune system (AIDs, after chemotherapy etc.) Herpes simplex also may cause colitis.

Ischemia is the term for poor blood flow (and therefore poor oxygen delivery) to tissues. Recently, more cases of acute ischemic colitis have been seen. The left side of the colon (descending and sigmoid colon) has a single blood vessel supply whereas the right colon (cecum, ascending and most of the transverse) has a redundant blood supply. If blood pressure drops too low or the single blood vessel becomes constricted or has narrowing from build up of cholesterol plaques the left colon can have too little blood flow and oxygen and become ischemic. It is like a “heart attack of the intestine” occurs. Abrupt onset of severe abdominal cramps associated with watery diarrhea followed by bloody diarrhea with the passage of mucus or tissue like material is the classic presentation. It is similar to the blood flow constriction that occurs normally in the uterus during a woman’s menstrual cycle that results in a “period” characterized by the passage of blood, clots, mucus, and tissue along with cramps. Risk factors for ischemic colitis include dehydration, certain medicines, smoking, presence of vascular disease (risk factors include smoking, diabetes, high blood pressure, high cholesterol, obesity, family history), travel to altitude, female hormone therapy, vigorous exercise and surgery or severe injury resulting in marked drop of blood pressure. The drugs usually associated are those that constrict the intestinal (mesenteric) blood vessels and/or cause either high or very low blood pressure like digoxin, cocaine, nasal decongestants, and NSAIDs like ibuprofen.

Cow’s milk protein allergy (CMPA) can cause colitis due to injury to the colon resulting from an allergic reaction to cow’s milk protein(s), usually casein. The resulting colitis is typically an eosinophilic colitis and occurs mostly in infants and young children. Cow’s milk protein colitis can be an acute severe colitis with pain (colic in infants) and bloody diarrhea or it may be microscopic (only diagnosed by biopsy) and associated with non-bloody diarrhea.

Radiation injury, especially rectal after treatment for prostate or female organ cancers, can cause a colitis localized to the rectum or radiation proctitis. It typically is associated with diarrhea that is usually bloody with urgency and fecal incontinence.

When the rectum or lower colon is diverted surgically to an external bag or colostomy the absence of stool and the bacteria within stool can cause what is termed diversion colitis.

Pouchitis is inflammation of a rectal pouch or small intestine pouch that is surgically created when the rectum is either bypassed or removed during the surgically treatment of cancer or chronic inflammatory bowel disease. A temporary rectal pouch may be created as the result of the need to bypass the intestine into a bag or colostomy. A pouch may be created to allow someone whose colon has been removed to avoid a bag or colostomy by connecting the small intestine to this loop of small bowel to ileal pouch anal anastomosis. A pouch may also be created by closing off the rectum below the colon resulting in a blind pouch that is diverted from the stream of feces from the intestine above.  Pouchitis can result from the lack of stool or feces containing good bacteria reaching a blind pouch.

Chronic idiopathic colitis usually takes the two major forms ulcerative colitis or Crohn’s colitis. They are idiopathic because the causes of UC and Crohn’s are not known.

Diverticulosis is the presence of sacs in the colon wall. When one or more of these diverticular sacs becomes inflamed, typically after obstruction of emptying of stool containing bacteria from the sac as the result of a large seed, nut or stool ball, diverticulitis has occurred. Diverticulitis is usually a localized process that is easily treated with antibiotics and not associated with inflammation of a significant segment of the colon lining.  However, diverticulosis can be associated with a variant of ulcerative colitis called diverticular associated colitis. This more commonly occurs in elderly people and may require surgery.

Chemotherapy can result in colitis due direct toxic effects. However, it is more commonly the result of chemotherapy induced low neutrophils or neutropenia. Neutrophils are the white blood cells that kill bacteria. Neutropenia allows colon bacteria to get through the intestine wall causing what is termed neutropenic colitis. When localized to the right colon or cecum, neutropenic colitis is also is called as typhilitis. Untreated kidney failure (uremia) has been described as causing colitis (uremic colitis) but is now rare because of the routine use of kidney dialysis.

Ulcerative colitis is a chronic idiopathic inflammatory bowel disease that is distinct from Crohn’s disease that can also affect the colon. When Crohn’s affects the colon only, it can be difficult to distinguish the two conditions. However, it is often important to do so because medical treatments and surgical approaches may be at times be different. Diagnosis of colitis and Crohn’s disease requires a sample of tissue from the intestinal tract usually obtained during colonoscopy. The availability of specific antibody blood tests or serologic markers has added significantly to the accuracy of screening, diagnosis and management of ulcerative colitis and Crohn’s disease.

Crohn’s disease is a specific inflammatory bowel disease of unknown cause that may affect the entire gastrointestinal tract. Crohn’s disease often affects the colon but usually affects the last segment of the small intestine known as the ileum with or without involvement of the colon and/or rectum.