By Dr Ananya Mandal, MD
Bowel movements are regulated by the muscles and nerves around the rectum, anus, sphincters (internal and external) as well as the pelvic floor muscles. The common factors that affect the normal bowel function leading to incontinence include:
inability of the rectum to hold the stool until social conditions permit evacuation
inability of the sphincters and muscles to hold the stool till appropriate time
damage to the nerves that send signals from the rectum to the brain normally allowing control of the bowel motions
Rectal muscles problems include:
Sphincters may be damaged due to injury during childbirth or due to other injuries. Nerve damage may occur due to spinal injuries, multiple sclerosis, spina bifida etc. 1-7
How does bowel incontinence occur?
There are two sets of sphincters or gates that control the stool movements in the rectum. If there is a problem or injury to the internal sphincter it may open automatically to let stools pass into the rectum. This causes the rectum to fill up and in turn leads to nerves of the rectal wall being stimulated leading to the brain giving signals for evacuation of bowel contents.
The external sphincter in these cases controls the bowel motions and prevents incontinence. In case of injury to the external sphincter as is common after a difficult vagina child birth, there may be leakage of stool and this leads to bowel incontinence in the long term. Vaginal delivery may lead to excessive stretching of the sphincter muscles and damage them. Forceps or assisted deliveries are also implicated.
Bowel or rectal surgery, fistula or fissure surgery, hemorrhoidectomy or piles surgery, manual dilatation of the sphincters, impaled injury to the anus and rectum are other causes of sphincter injury and damage.
Causes of bowel incontinence
Causes of bowel incontinence thus includes diarrhea, severe constipation and so forth.
Diarrhea and bowel incontinence
In diarrhea the rectum is unable to hold the stool as it has large amounts of water in it. Those with conditions that lead to diarrhea like irritable bowel syndrome (IBS), Crohn’s disease or ulcerative colitis that lead to inflammation of the digestive system and the large bowel may also have diarrhea leading to bowel incontinence.
Inflammatory conditions also lead to rectal scarring and bowel incontinence.
Severe constipation and bowel incontinence
Severe constipation may lead to hard and large quantities of stool to be stuck in the rectum. This is called faecal impaction.
The stool then begins to stretch the muscles of the rectum and makes them weak. This leads to incontinence of the bowel.
Rectum cancer and bowel incontinence
Rectum cancer or tumors also make the rectal muscles weak and may lead to bowel incontinence.
Nerve damage of bowel incontinence
Nerve damage may lead to bowel incontinence. Muscle and nerve damage is common among frail elderly individuals. Other conditions that predispose to nerve damage include:
Nerve and muscle damage may also be seen after radiation therapy or colon surgery for colon or rectum cancer. Those with urinary incontinence are at a high risk of bowel incontinence as well. This could be associated with the nerves around the pelvic muscles.
Severe cognitive loss and bowel incontinence
Bowel control may also be lost in individuals with severe cognitive loss and dementia. This includes those with learning disabilities, Alzheimer’s disease etc.
Other causes of bowel incontinence
Poor overall health, severe malnutrition, multiple chronic, or long-lasting, illnesses may also lead to bowel incontinence.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)
Last Updated: Sep 10, 2012