Causes of Fecal Incontinence

Fecal incontinence can have several causes:

• Constipation
  
  
• damage to the anal sphincter muscles
  
  
• damage to the nerves of the anal sphincter muscles or the rectum
  
  
• loss of storage capacity in the rectum
  
  
• diarrhea
  
  
• pelvic floor dysfunction

Constipation

Constipation is one of the most common causes of fecal incontinence. Constipation causes large, hard stools to become lodged in the rectum. Watery stool can then leak out around the hardened stool. Constipation also causes the muscles of the rectum to stretch, which weakens the muscles so they can't hold stool in the rectum long enough for a person to reach a bathroom.

Muscle Damage

Fecal incontinence can be caused by injury to one or both of the ring-like muscles at the end of the rectum called the anal internal and/or external sphincters. The sphincters keep stool inside. When damaged, the muscles aren't strong enough to do their job, and stool can leak out. In women, the damage often happens when giving birth. The risk of injury is greatest if the doctor uses forceps to help deliver the baby or does an episiotomy, which is a cut in the vaginal area to prevent it from tearing during birth. Hemorrhoid surgery can damage the sphincters as well.

Nerve Damage

Fecal incontinence can also be caused by damage to the nerves that control the anal sphincters or to the nerves that sense stool in the rectum. If the nerves that control the sphincters are injured, the muscle doesn't work properly and incontinence can occur. If the sensory nerves are damaged, they don't sense that stool is in the rectum. You then won't feel the need to use the bathroom until stool has leaked out. Nerve damage can be caused by childbirth, a long-term habit of straining to pass stool, stroke, and diseases that affect the nerves, such as diabetes and multiple sclerosis.

Loss of Storage Capacity

Normally, the rectum stretches to hold stool until you can get to a bathroom. But rectal surgery, radiation treatment, and inflammatory bowel disease can cause scarring that makes the walls of the rectum stiff and less elastic. The rectum then can't stretch as much and can't hold stool, and fecal incontinence results. Inflammatory bowel disease also can make rectal walls very irritated and thereby unable to contain stool.

Diarrhea

Diarrhea, or loose stool, is more difficult to control than solid stool that is formed. Even people who don't have fecal incontinence can have an accident when they have diarrhea.

Pelvic Floor Dysfunction

Abnormalities of the pelvic floor can lead to fecal incontinence. Examples of some abnormalities are decreased perception of rectal sensation, decreased anal canal pressures, decreased squeeze pressure of the anal canal, impaired anal sensation, a dropping down of the rectum (rectal prolapse), protrusion of the rectum through the vagina (rectocele), and/or generalized weakness and sagging of the pelvic floor. Often the cause of pelvic floor dysfunction is childbirth, and incontinence doesn't show up until the midforties or later.

source: http://digestive.niddk.nih.gov/ddiseases/pubs/fecalincontinence/index.htm