Types of Colitis and Causes of Large Bowel (Colon) Inflammation

Colitis is the medical term for inflammation of the colon and may include the first part of the large intestine known as the cecum. The colon plays an important role in the uptake of water from the intestinal contents, storage, processing and evacuation of waste matter and the absorption of vitamin K created by colonic bacteria. Inflammation disrupts the normal functioning of the colon, giving rise to symptoms like diarrhea, leading to dehydration and even vitamin deficiencies in the chronic setting. The inflammatory process may involve the small intestine (enteritis) or extend to the rectum (proctitis).

Causes of Different Types of Colitis

In colitis, it is primarily the inner mucosal lining of the colon that is inflamed along with the underlying submucosa. However, in certain types of colitis, the inflammation and subsequent disease processes like ischemia and necrosis may extend through the entire wall of the colon.

Infectious Colitis

In this type of colitis, the large bowel is infected with pathogens or disrupted by an overgrowth of certain types of normal intestinal bacteria.  These pathogenic microorganisms may be bacteria, viruses or parasites. It often involves the small intestine as well and is known as infectious enterocolitis. Pseudomembranous colitis also falls within this type of colitis as it arises due to an overgrowth of Clostridium difficile often following antibiotic use.

Ischemic Colitis

This type of colitis arises when the blood supply to the colon is compromised. It may be due to various factors including conditions like athersclerosis, cardiac conditions or strangulation of the bowel – volvulus or incarcerated hernia. It is also known as ischemic bowel disease. Other types of enterocolitis which also arise due to ischemia includes radiation enterocolitis and necrotizing enterocolitis.

• Radiation enterocolitis is a result of the bowels being irradiated, usually as a means to treat a cancerous growth in the abdomen or pelvis. The radiation may damage the blood vessels of the colon thereby leading to colitis.
• Necrotizing enterocolitis is a serious disorder seen in newborn babies. Mucosal injury and ischemia may be a result of several causes including an immature immune system, colonic bacteria and feeding, more likely formula feeding than breastfeeding.

Inflammatory Bowel Disease

The exact cause of inflammatory bowel disease is unknown. The two types of inflammatory bowel disease, ulcerative colitis and Crohn’s disease, appear to arise due to autoimmune factors. In ulcerative colitis, there is inflammation and ulceration of the colon and/or rectum possibly due to overactivity of the body’s immune system. Crohn’s disease can affect any part of the gastrointestinal tract but is more likely to occur in the small intestine and colon. Inflammation and granuloma formation in Crohn’s disease may affect short segments of the bowel surrounded by normal and healthy tissue. The similarity of ulcerative colitis and Crohn’s disease may sometimes blur the distinction between these two types of colitis and it is then referred to as indeterminate colitis.

Microscopic Colitis

This type of colitis also occurs for unknown reasons. The wall of the colon is inflamed with higher than normal concentrations of lymphoyctes in the epithelial layer. There are two types of microscopic colitis – collagenous and lymphocytic. Both are histologically similar but in collagenous colitis, there is thickening of the subepithelial collagen layer which is not observed in lymphocytic colitis.