Colitis (also known as colonitis) is an inflammation of the colon. It is a digestive disorder. There are several different types and causes of colitis, including:

1. Ulcerative colitis

Ulcerative colitis is an inflammatory disease of the bowel, that usually affects the distal end of the large intestine and rectum. It has no known cause, although there is a genetic component to susceptibility.

Ulcerative colitis is similar to Crohn's disease, but there are characteristic differences. Ulcerative colitis affects only the colon and cannot "migrate" to the small intestine, while Chron's disease can affect the entire digestive tract. Complete colon removal can thus be considered a "cure" for ulcerative colitis. Ulcerative colitis is usually confined to the mucosal and submucosal lining of the colon, and affects whole areas of intestine. Crohn's disease, on the other hand tends to be patchy, and affect more layers of intestine, being transmural in nature. Due to the nature of the inflammation, Ulcerative colitis rarely requires resection surgery in contrast to Chron's disease where such surgery is often needed due to dangerous bowel obstructions and other complications. However, the risk of colorectal cancer development in ulcerative colitis patients is significantly greater (up to 5 times) than general population after 10 years following the diagnosis.

2. Pseudomembranous colitis

Pseudomembranous colitis is a infection of the colon caused by the bacterium Clostridium difficile. The illness is characterized by diarrhea, fever, and  abdominal pain. It can be severe and even fatal.

In most cases the patient had recently been on antibiotics. Antibiotics disturb the normal bowel bacterial flora that generally keeps the bacteria Clostridium difficile under control. Clindamycin is the antibiotic associated with this disorder classically, but any antibiotic can cause the condition. Additional groups at increased risk are diabetics and the elderly. Half of cases are not associated with risk factors.

The disease is ususally treated with metronidazole. Oral vancomycin is an alternative drug. Occasionally metronidazole has been associated with the development of pseudomembranous colitis. In these cases metronidazole is still effective treatment, since the cause of the colitis is not the antibiotic, but rather the change in bacterial flora from a previous round of antibiotics. If antibiotics do not control the infection the patient may require a colectomy (removal of the colon) for treatment of the colitis.

3. Irritable bowel syndrome

In medicine (gastroenterology), irritable bowel syndrome (IBS) is a group of functional bowel disorders which are fairly common and make up 20–50% of visits to a specialist.

Features

Symptoms of IBS are abdominal pain or discomfort associated with changes in bowel habits in the absence of any structural abnormality. Colonic hypersensitivity is a sensitive but less specific sign of IBS. Depending on the kind of discomfort and bowel habits, IBS is also known as spastic colon, and can be subclassified into diarrhea-predominant (IBS-D), constipation-predominant (IBS-C) and IBS with alternating stool pattern (IBS-A). Typical is the overlap of IBS with chronic pelvic pain, fibromyalgia and  mental disorder.

4. Fulminant colitis

Fulminant colitis is characterized by:

• sever bloody diarrhea
• fever
• hypovolemia
• anemia

It is seen in 5-15% ulcerative colitis patients